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Author SHA1 Message Date
SJ Park
954157679e mm/damon/core: disallow overlapping input ranges for damon_set_regions() 
damon_set_regions() assumes the input ranges are sorted by the address and
don't overlap each other.  Hence the assumption was initially to be
explicitly validated.  But commit 97d482f459 ("mm/damon/sysfs: reuse
damon_set_regions() for regions setting") has mistakenly removed the
validation.

This can make DAMON behave in unexpected ways.  At the best, the
monitoring results snapshot will just look weird since there will be
overlapping regions.  DAMOS will also work weirdly, applying the same
action multiple times for overlapping regions, and make DAMOS quota weird.
More seriously, depending on the setup and regions updates sequence,
negative size regions can be made.  It will trigger WARN_ONCE() if the
kernel is built with CONFIG_DAMON_DEBUG_SANITY=y.  Depending on the
monitoring results, the negative size region can further trigger division
by zero in damon_merge_two_regions().

Note that some of the consequences including the WARN_ONCE() and the
divide by zero depend on commits that were introduced after the root cause
commit 97d482f459 ("mm/damon/sysfs: reuse damon_set_regions() for
regions setting").

Fix the problems by checking the assumption and returning an error if
the input ranges don't meet the assumption.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260703165610.92894-1-sj@kernel.org
Link: https://lore.kernel.org/20260630041806.151124-1-sj@kernel.org [1]
Fixes: 97d482f459 ("mm/damon/sysfs: reuse damon_set_regions() for regions setting")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.19.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-07-09 15:48:55 -07:00
SJ Park
1292c0ecb1 mm/damon/core: validate ranges in damon_set_regions() 
DAMON core logic assumes zero length regions don't exist.  However, a few
DAMON API callers including DAMON_SYSFS, DAMON_RECLAIM and DAMON_LRU_SORT
allow users to set empty monitoring target regions.  This could result in
WARN_ONCE() on CONFIG_DAMON_DEBUG_SANITY enabled kernel, and
divide-by-zero from damon_merge_two_regions().

For example, the WANR_ONCE() can be triggered like below.

    # grep DAMON_DEBUG_SANITY /boot/config-$(uname -r)
    # CONFIG_DAMON_DEBUG_SANITY=y
    # damo start
    # cd /sys/kernel/mm/damon/admin/kdamonds/0
    # echo 0 > contexts/0/targets/0/regions/0/start
    # echo 0 > contexts/0/targets/0/regions/0/end
    # echo commit > state
    # dmesg
    [....]
    [   73.705780] ------------[ cut here ]------------
    [   73.707552] start 0 >= end 0
    [   73.708452] WARNING: mm/damon/core.c:359 at damon_new_region+0x6e/0x80, CPU#1: kdamond.0/758
    [...]

All DAMON API callers eventually use damon_set_regions() to setup the
regions.  Add the validation logic in the function.

Link: https://lore.kernel.org/20260630035221.146458-1-sj@kernel.org
Fixes: 43b0536cb4 ("mm/damon: introduce DAMON-based Reclamation (DAMON_RECLAIM)")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Yang yingliang <yangyingliang@huawei.com>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-07-09 15:48:54 -07:00
SJ Park
14afcf67dc MAINTAINERS: s/SeongJae/SJ/ 
My legal and preferred first names are SeongJae and SJ, respectively.  I
was using the legal name for commits and tags, while using the preferred
name for conversations.  It sometimes confuses people including myself. 
Consistently use the preferred name.

Together remove copyright notes on files.  Those are only confusing for
people who are not familiar with the law.  Meanwhile, we can infer the
information in a better way from git logs and public information.

Link: https://lore.kernel.org/20260630013820.143366-1-sj@kernel.org
Signed-off-by: SJ Park <sj@kernel.org>
Acked-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-07-09 15:48:53 -07:00
SeongJae Park
6a66c557a2 mm/damon/core: always put unsuccessfully committed target pids 
damon_commit_target() puts and gets the destination and the source target
pids.  It puts the destination target pid because it will be overwritten
by the source target pid.  It gets the source pid because the caller is
supposed to eventually put the pids.  In more detail, the caller will call
damon_destroy_ctx() after damon_commit_ctx() to destroy the entire source
context.  And in this case, [f]vaddr operation set's cleanup_target()
callback will put the pids.

The commit operation is made at the context level.  The operation can fail
in multiple places including in the middle and after the targets commit
operations.  For any such failures, immediately the error is returned to
the damon_commit_ctx() caller.  If some or all of the source target pids
were committed to the destination during the unsuccessful context commit
attempt, those pids should be put twice.

The source context will do the put operations using the above explained
routine.  However, let's suppose the destination context was not
originally using [f]vaddr operation set and the commit failed before the
ops of the source context is committed.  The destination does not have the
cleanup_target() ops callback, so it cannot put the pids via the
damon_destroy_ctx().

As a result, the pids are leaked.  The issue in the real world would be
not very common.  The commit feature is for changing parameters of running
DAMON context while inheriting internal status like the monitoring
results.  The monitoring results of a physical address range ain't have
things that are beneficial to be inherited to a virtual address ranges
monitoring.  So the problem-causing DAMON control would be not very common
in the real world.  That said, it is a supported feature.  And
damon_commit_target() failure due to memory allocation is relatively
realistic [1] if there are a huge number of target regions.

Fix by putting the pids in the commit operation in case of the failures.

The issue was discovered [2] by Sashiko.

Link: https://lore.kernel.org/20260605013849.83750-1-sj@kernel.org
Link: https://lore.kernel.org/20260603112306.58490-1-akinobu.mita@gmail.com [1]
Link: https://lore.kernel.org/20260320020056.835-1-sj@kernel.org [2]
Fixes: 83dc7bbaec ("mm/damon/sysfs: use damon_commit_ctx()")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.11.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-21 11:37:36 -07:00
SeongJae Park
7e6cc35f52 mm/damon/core: trace esz at first setup 
DAMON traces effective size quota from the second update, only if a change
has been made by the update.  Tracing only changed updates was an
intentional decision to avoid unnecessary same value tracing.  Always
skipping the first value is just an unintended mistake.

The mistake makes the tracepoint based investigation incomplete, because
the first effective size quota is never traced.  It is not a big issue
when the 'consist' quota tuner is used, because it keeps changing the
quota in the usual setup.

However, when the 'temporal' tuner is used, the quota value is not changed
before the goal achievement status is completely changed.  For example, if
the DAMOS scheme is started with an under-achieved goal, the quota is set
to the maximum value, and kept the same value until the goal is achieved. 
Because DAMON skips the first value, the user cannot know what effective
quota the current scheme is using.  Only after the goal is achieved, the
effective quota is changed to zero, and traced.

Unconditionally trace the initial quota value to fix this problem.

Note that the 'temporal' quota tuner was introduced by commit af738a6a00
("mm/damon/core: introduce DAMOS_QUOTA_GOAL_TUNER_TEMPORAL"), which was
added to 7.1-rc1.  But even with the 'consist' quota tuner, the tracing is
unintentionally incomplete.  Hence this commit marks the introduction of
the trace event as the broken commit.

Link: https://lore.kernel.org/20260520150311.80925-1-sj@kernel.org
Fixes: a86d695193 ("mm/damon: add trace event for effective size quota")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.17.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:02 -07:00
SeongJae Park
b8db646fe9 mm/damon/core: remove damon_verify_nr_regions() 
When CONFIG_DAMON_DEBUG_SANITY is enabled, damon_verify_nr_regions() is
called for each damon_nr_regions() invocation.  damon_veify_nr_regions()
iterates all regions.  damon_nr_regions() is called for each region in
kdamond_reset_aggregated() and damos_apply_scheme().  Hence it imposes
O(n**2) overhead where n is the number of regions.

Though the verification is enabled only under DAMON_DEBUG_SANITY, which is
not for production use cases, it could be too high overhead.  Meanwhile,
damon_verify_ctx() is doing the damon_nr_regions() test.  Because
damon_verify_ctx() is called for each kdamond_call(), the test coverage
from damon_verify_ctx() could be sufficient.  Remove damon_nr_regions()
verification.

Link: https://lore.kernel.org/20260522154026.80546-10-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:01 -07:00
SeongJae Park
8f793f1ad5 mm/damon/core: add kdamond_call() debug_sanity check 
kdamond_call() is the place where DAMON API callers are allowed to access
the DAMON context's public internal state including the monitoring
results.  Hence it is important to ensure it is called with the expected
DAMON context state.  Do the check under DAMON_DEBUG_SANITY.

Link: https://lore.kernel.org/20260522154026.80546-9-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:01 -07:00
SeongJae Park
50d2dec8af mm/damon/core: hide damon_destroy_region() 
damon_destroy_region() is being used by only DAMON core, but exposed to
DAMON API callers.  Exposing something that is not really being used by
others will only increase the maintenance cost.  Hide it.

Link: https://lore.kernel.org/20260522154026.80546-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:01 -07:00
SeongJae Park
26d6f6960f mm/damon/core: hide damon_insert_region() 
damon_insert_region() is being used by only DAMON core, but exposed to
DAMON API callers.  Exposing something that is not really being used by
others will only increase the maintenance cost.  Hide it.

Link: https://lore.kernel.org/20260522154026.80546-7-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:01 -07:00
SeongJae Park
9cf7ef2d66 mm/damon/core: hide damon_add_region() 
damon_add_region() is being used by only DAMON core, but exposed to DAMON
API callers.  Exposing something that is not really being used by others
will only increase the maintenance cost.  Hide it.

Link: https://lore.kernel.org/20260522154026.80546-6-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:00 -07:00
SeongJae Park
b23dbda659 mm/damon/core: do not use region out of a loop in damon_set_regions() 
damon_set_regions() assumes the DAMON region iterator is referencing the
last region after the region iteration loop is completed.  The code is
indeed implemented in the way, but that is not a documented safe behavior.
Hence it is unreliable and difficult to read.  Cleanup the code to avoid
the case.

No behavioral change is intended.

Link: https://lore.kernel.org/20260522154026.80546-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:00 -07:00
SeongJae Park
ce71e5aa8d mm/damon/core: safely handle no region case in damon_set_regions() 
Patch series "mm/damon: minor improvements for code readability and tests".

Implement minor improvements on code readability and tests for DAMON.

First seven patches are for DAMON code readability and resulting
maintenance.  Patches 1 and 2 make damon_set_regions() safer and easier to
read.  Patches 3 and 4 remove fragmented DAMON API use cases.  Patches 5-7
hides unused core functions that are unnecessarily exposed to API callers.

The following seven patches are for DAMON tests improvement.  Patches 8
and 9 adds and removes DAMON_DEBUG_SANITY verifications to ensure
reasonable test coverage without too high overhead.  Patch 10 adds a new
kunit test for damon_set_regions().  Patch 11 makes sysfs.py selftest more
gracefully finishes under test failures.  Patches 12-13 adds simple
sysfs.sh test cases for the monitoring intervals goal directory, the
addr_unit file and the pause file.


This patch (of 14):

damon_set_regions() calls damon_first_region() regardless of the number of
DAMON regions in a given DAMON target.  damon_first_region() internally
uses list_first_entry(), which clearly documents the list is expected to
be not empty.  Due to the internal implementation of the macro,
damon_set_regions() is safe for now.  But the internal implementation of
the macro can be changed in future.  Refactor the function to explicitly
and safely handle the empty region list case without depending on the
internal implementation.

No behavioral change is intended.

Link: https://lore.kernel.org/20260522154026.80546-1-sj@kernel.org
Link: https://lore.kernel.org/20260522154026.80546-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-04 14:45:00 -07:00
niecheng
e186709b0a mm/damon/core: clarify next_intervals_tune_sis update path 
Patch series "mm/damon: documentation and comment fixes".


This patch (of 3):

damon_set_attrs() updates next_aggregation_sis and next_ops_update_sis for
online attrs updates, but it does not update next_intervals_tune_sis
there.

This can look like a missing update when reading damon_set_attrs() alone,
while next_intervals_tune_sis is actually updated in kdamond_fn().

Add a short comment to make this explicit.

Link: https://lore.kernel.org/20260520012104.93602-1-sj@kernel.org
Link: https://lore.kernel.org/20260520012104.93602-2-sj@kernel.org
Suggested-by: SeongJae Park <sj@kernel.org>
Signed-off-by: niecheng <niecheng1@uniontech.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Sakurai Shun <ssh1326@icloud.com>
Cc: Zenghui Yu <zenghui.yu@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:34 -07:00
SeongJae Park
543ab01db7 mm/damon/sysfs: setup damon_filter->memcg_id from path 
Find and set the memcg_id for damon_filter from the user-passed memory
cgroup path when updating the DAMON input parameters.

Link: https://lore.kernel.org/20260518234119.97569-27-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:31 -07:00
SeongJae Park
d9f23f2f82 mm/damon/core: introduce DAMON_FILTER_TYPE_MEMCG 
Belonging memory cgoup is another data attribute that can be useful to
monitor.  Introduce a new DAMON filter type, namely
DAMON_FILTER_TYPE_MEMCG, for monitoring of this attribute.

Link: https://lore.kernel.org/20260518234119.97569-23-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:30 -07:00
SeongJae Park
b9b7bad279 mm/damon: trace probe_hits 
Introduce a new tracepoint for exposing the per-region per-probe positive
sample count via tracefs.

Link: https://lore.kernel.org/20260518234119.97569-19-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:29 -07:00
SeongJae Park
9b1f8c8d01 mm/damon/core: do data attributes monitoring 
Implement the data attributes monitoring execution.  Update kdamond to
invoke the probes application callback, and reset the aggregated number of
per-region per-probe positive samples for every aggregation interval.

Link: https://lore.kernel.org/20260518234119.97569-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:26 -07:00
SeongJae Park
57c6332f25 mm/damon/core: introduce damon_region->probe_hits 
Add an array for the per-region per-probe positive samples count.  For
simple and efficient implementation, add a limit to the number of data
probes and set the array to support only the limited number of counters.

Link: https://lore.kernel.org/20260518234119.97569-6-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:25 -07:00
SeongJae Park
d0de4b29c7 mm/damon/core: commit probes 
Update damon_commit_ctx() to commit installed data probes, too.

Link: https://lore.kernel.org/20260518234119.97569-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:25 -07:00
SeongJae Park
f557693dd8 mm/damon/core: introduce damon_filter 
Define a data structure for constructing damon_probe's attributes check,
namely damon_filter.  It is very similar to damos_filter but works only
for monitoring purposes.  Also embed that into damon_probe, implement
essential handling of the link, with fundamental helpers.

Link: https://lore.kernel.org/20260518234119.97569-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:25 -07:00
SeongJae Park
18c777859f mm/damon/core: embed damon_probe objects in damon_ctx 
Let damon_probe objects be able to be installed on a given damon_ctx, by
adding a linked list header for storing the objects.  Add initialization
and cleanup of the new field with helper functions, too.

Link: https://lore.kernel.org/20260518234119.97569-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:25 -07:00
Jiayuan Chen
9012c4e647 mm/damon: replace damon_rand() with a per-ctx lockless PRNG 
damon_rand() on the sampling_addr hot path called get_random_u32_below(),
which takes a local_lock_irqsave() around a per-CPU batched entropy pool
and periodically refills it with ChaCha20.  At elevated nr_regions counts
(20k+), the lock_acquire / local_lock pair plus __get_random_u32_below()
dominate kdamond perf profiles.

Replace the helper with a lockless lfsr113 generator (struct rnd_state)
held per damon_ctx and seeded from get_random_u64() in damon_new_ctx(). 
kdamond is the single consumer of a given ctx, so no synchronization is
required.  Range mapping uses traditional reciprocal multiplication,
similar as get_random_u32_below(); for spans larger than U32_MAX (only
reachable on 64-bit) the slow path combines two u32 outputs and uses
mul_u64_u64_shr() at 64-bit width.  On 32-bit the slow path is dead code
and gets eliminated by the compiler.

The new helper takes a ctx parameter; damon_split_regions_of() and the
kunit tests that call it directly are updated accordingly.

lfsr113 is a linear PRNG and MUST NOT be used for anything
security-sensitive.  DAMON's sampling_addr is not exposed to userspace and
is only consumed as a probe point for PTE accessed-bit sampling, so a
non-cryptographic PRNG is appropriate here.

Tested with paddr monitoring and max_nr_regions=20000: kdamond CPU usage
reduced from ~72% to ~50% of one core.

Link: https://lore.kernel.org/20260505145212.108644-1-jiayuan.chen@linux.dev
Link: https://lore.kernel.org/damon/20260426173346.86238-1-sj@kernel.org/T/#m4f1fd74112728f83a41511e394e8c3fef703039c
Link: https://lore.kernel.org/20260509011816.85145-1-sj@kernel.org
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Shu Anzai <shu17az@gmail.com>
Cc: Quanmin Yan <yanquanmin1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-06-02 15:22:09 -07:00
SeongJae Park
3a870b4377 mm/damon/core: remove damon_set_region_biggest_system_ram_default() 
Now nobody is using damon_set_region_biggest_system_ram_default().  Remove
it.

Link: https://lore.kernel.org/20260429041232.90257-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:05:02 -07:00
SeongJae Park
70d8797c15 mm/damon: introduce damon_set_region_system_rams_default() 
Patch series "mm/damon/reclaim,lru_sort: monitor all system rams by
default".

DAMON_RECLAIM and DAMON_LRU_SORT set the biggest 'System RAM' resource of
the system as the default monitoring target address range.  The main
intention behind the design is to minimize the overhead coming from
monitoring of non-System RAM areas.

This could result in an odd setup when there are multiple discrete System
RAMs of considerable sizes.  For example, there are System RAMs each
having 500 GiB size.  In this case, only the first 500 GiB will be set as
the monitoring region by default.  This is particularly common on NUMA
systems.  Hence the modules allow users to set the monitoring target
address range using the module parameters if the default setup doesn't
work for them.  In other words, the current design trades ease of setup
for lower overhead.

However, because DAMON utilizes the sampling based access check and the
adaptive regions adjustment mechanisms, the overhead from the monitoring
of non-System RAM areas should be negligible in most setups.  Meanwhile,
the setup complexity is causing real headaches for users who need to run
those modules on various types of systems.  That is, the current tradeoff
is not a good deal.

Set the physical address range that can cover all System RAM areas of the
system as the default monitoring regions for DAMON_RECLAIM and
DAMON_LRU_SORT.

Technically speaking, this is changing documented behavior.  However, it
makes no sense to believe there is a real use case that really depends on
the old weird default behavior.  If the old default behavior was working
for them in the reasonable way, this change will only add a negligible
amount of monitoring overhead.  If it didn't work, the users may already
be using manual monitoring regions setup, and they will not be affected by
this change.

Patches Sequence
================

Patch 1 introduces a new core function that will be used for the new
default monitoring target region setup.  Patch 2 and 3 update
DAMON_RECLAIM and DAMON_LRU_SORT to use the new function instead of the
old one, respectively.  Patch 4 removes the old core function that was
replaced by the new one, as there is no more user of it.  Patch 5 updates
DAMON_STAT to use the new one instead of its in-house nearly-duplicate
self implementation of the functionality.  Finally patches 6 and 7 update
the DAMON_RECLAIM and DAMON_LRU_SORT user documentation for the new
behaviors, respectively.


This patch (of 7):

damon_set_region_biggest_system_ram_default() sets the monitoring target
region as the caller requested.  If the caller didn't specify the region,
it finds the biggest System RAM of the system and sets it as the target
region.  When there are more than one considerable size of System RAM
resources in the system, the default target setup makes no sense. 
Introduce a variant, namely damon_set_region_system_rams_default().  It
sets a physical address range that covers all System RAM resources as the
default target region.

Link: https://lore.kernel.org/20260429041232.90257-1-sj@kernel.org
Link: https://lore.kernel.org/20260429041232.90257-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:05:01 -07:00
SeongJae Park
3b9e3cc040 mm/damon/core: introduce damon_ctx->paused 
Patch series "mm/damon: let DAMON be paused and resumed", v2.

DAMON utilizes a few mechanisms that enhance itself over time.  Adaptive
regions adjustment, goal-based DAMOS quota auto-tuning and monitoring
intervals auto-tuning like self-training mechanisms are such examples.  It
also adds access frequency stability information (age) to the monitoring
results, which makes it enhanced over time.

Sometimes users have to stop DAMON.  In this case, DAMON internal state
that enhanced over the time of the last execution simply goes away. 
Restarted DAMON have to train itself and enhance its output from the
scratch.  This makes DAMON less useful in such cases.  Introducing three
such use cases below.

Investigation of DAMON.  It is best to do the investigation online,
especially when it is a production environment.  DAMON therefore provides
features for such online investigations, including DAMOS stats, monitoring
result snapshot exposure, and multiple tracepoints.  When those are
insufficient, and there are additional clues that could be interfered by
DAMON, users have to temporarily stop DAMON to collect the additional
clues.  It is not very useful since many of DAMON internal clues are gone
when DAMON is stopped.  The loss of the monitoring results that improved
over time is also problematic, especially in production environments.

Monitoring of workloads that have different user-known phases.  For
example, in Android, applications are known to have very different access
patterns and behaviors when they are running on the foreground and the
background.  It can therefore be useful to separate monitoring of apps
based on whether they are running on the foreground and on the background.
Having two DAMON threads per application that paused and resumed for the
apps foreground/background switches can be useful for the purpose.  But
such pause/resume of the execution is not supported.

Tests of DAMON.  A few DAMON selftests are using drgn to dump the internal
DAMON status.  The tests show if the dumped status is the same as what the
test code expected.  Because DAMON keeps running and modifying its
internal status, there are chances of data races that can cause false test
results.  Stopping DAMON can avoid the race.  But, since the internal
state of DAMON is dropped, the test coverage will be limited.

Let DAMON execution be paused and resumed without loss of the internal
state, to overhaul the limitations.  For this, introduce a new DAMON
context parameter, namely 'pause'.  API callers can update it while the
context is running, using the online parameters update functions
(damon_commit_ctx() and damon_call()).  Once it is set, kdamond_fn() main
loop will do only limited works excluding the monitoring and DAMOS works,
while sleeping sampling intervals per the work.  The limited works include
handling of the online parameters update.  Hence users can unset the
'pause' parameter again.  Once it is unset, kdamond_fn() main loop will do
all the work again (resumed).  Under the paused state, it also does stop
condition checks and handling of it, so that paused DAMON can also be
stopped if needed.  Expose the feature to the user space via DAMON sysfs
interface.  Also, update existing drgn-based tests to test and use the
feature.

Tests
=====

I confirmed the feature functionality using real time tracing ('perf
trace' or 'trace-cmd stream') of damon:damon_aggregated DAMON tracepoint. 
By pausing and resuming the DAMON execution, I was able to see the trace
stops and continued as expected.  Note that the pause feature support is
added to DAMON user-space tool (damo) after v3.1.9.  Users can use
'--pause_ctx' command line option of damo for that, and I actually used it
for my test.  The extended drgn-based selftests are also testing a part of
the functionality.

Patches Sequence
================

Patch 1 introduces the new core API for the pause feature.  Patch 2 extend
DAMON sysfs interface for the new parameter.  Patches 3-5 update design,
usage and ABI documents for the new sysfs file, respectively.  The
following five patches are for tests.  Patch 6 implements a new kunit test
for the pause parameter online commitment.  Patches 7 and 8 extend DAMON
selftest helpers to support the new feature.  Patch 9 extends selftest to
test the commitment of the feature.  Finally, patch 10 updates existing
selftest to be safe from the race condition using the pause/resume
feature.


This patch (of 10):

DAMON supports only start and stop of the execution.  When it is stopped,
its internal data that it self-trained goes away.  It will be useful if
the execution can be paused and resumed with the previous self-trained
data.

Introduce per-context API parameter, 'paused', for the purpose.  The
parameter can be set and unset while DAMON is running and paused, using
the online parameters commit helper functions (damon_commit_ctx() and
damon_call()).  Once 'paused' is set, the kdamond_fn() main loop does only
limited works with sampling interval sleep during the works.  The limited
works include the handling of the online parameters update, so that users
can unset the 'pause' and resume the execution when they want.  It also
keep checking DAMON stop conditions and handling of it, so that DAMON can
be stopped while paused if needed.

Link: https://lore.kernel.org/20260427151231.113429-1-sj@kernel.org
Link: https://lore.kernel.org/20260427151231.113429-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:04:57 -07:00
SeongJae Park
4ee4fb3214 mm/damon/core: introduce failed region quota charge ratio 
DAMOS quota is charged to all DAMOS action application attempted memory,
regardless of how much of the memory the action was successful and failed.
This makes understanding quota behavior without DAMOS stat but only with
end level metrics (e.g., increased amount of free memory for DAMOS_PAGEOUT
action) difficult.  Also, charging action-failed memory same as
action-successful memory is somewhat unfair, as successful action
application will induce more overhead in most cases.

Introduce DAMON core API for setting the charge ratio for such
action-failed memory.  It allows API callers to specify the ratio in a
flexible way, by setting the numerator and the denominator.

Link: https://lore.kernel.org/20260428013402.115171-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:04:42 -07:00
SeongJae Park
2423bb5fbe mm/damon/core: merge regions after applying DAMOS schemes 
damos_apply_scheme() could split the given region if applying the scheme's
action to the entire region can result in violating the quota-set upper
limit.  Keeping regions that are created by such split operations is
unnecessary overhead.

The overhead would be negligible in the common case because such split
operations could happen only up to the number of installed schemes per
scheme apply interval.  The following commit could make the impact larger,
though.  The following commit will allow the action-failed region to be
charged in a different ratio.  If both the ratio and the remaining quota
is quite small while the region to apply the scheme is quite large and the
action is nearly always failing, a high number of split operations could
happen.

Remove the unnecessary overhead by merging regions after applying schemes
is done for each region.  The merge operation is made only if it will not
lose monitoring information and keep min_nr_regions constraint.  In the
worst case, the max_nr_regions could still be violated until the next
per-aggregation interval merge operation is made.

Link: https://lore.kernel.org/20260428013402.115171-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:04:42 -07:00
SeongJae Park
c7ec7d5f6b mm/damon/core: handle <min_region_sz remaining quota as empty 
Patch series "mm/damon: introduce DAMOS failed region quota charge ratio".

Let users set different DAMOS quota charge ratios for DAMOS action failed
regions, for deterministic and consistent DAMOS action progress.

Common Reports: Unexpectedly Slow DAMOS
=======================================

One common issue report that we get from DAMON users is that DAMOS action
applying progress speed is sometimes much slower than expected.  And one
common root cause is that the DAMOS quota is exceeded by the action
applying failed memory regions.

For example, a group of users tried to run DAMOS-based proactive memory
reclamation (DAMON_RECLAIM) with 100 MiB per second DAMOS quota.  They ran
it on a system having no active workload which means all memory of the
system is cold.  The expectation was that the system will show 100 MiB per
second reclamation until (nearly) all memory is reclaimed.  But what they
found is that the speed is quite inconsistent and sometimes it becomes
very slower than the expectation, sometimes even no reclamation at all for
about tens of seconds.  The upper limit of the speed (100 MiB per second)
was being kept as expected, though.

By monitoring the qt_exceeds (number of DAMOS quota exceed events) DAMOS
stat, we found DAMOS quota is always exceeded when the speed is slow.  By
monitoring sz_tried and sz_applied (the total amount of DAMOS action tried
memory and succeeded memory) DAMOS stats together, we found the
reclamation attempts nearly always failed when the speed is slow.

DAMOS quota charges DAMOS action tried regions regardless of the
successfulness of the try.  Hence in the example reported case, there was
unreclaimable memory spread around the system memory.  Sometimes nearly
100 MiB of memory that DAMOS tried to reclaim in the given quota interval
was reclaimable, and therefore showed nearly 100 MiB per second speed. 
Sometimes nearly 99 MiB of memory that DAMOS was trying to reclaim in the
given quota interval was unreclaimable, and therefore showing only about 1
MiB per second reclaim speed.

We explained it is an expected behavior of the feature rather than a bug,
as DAMOS quota is there for only the upper-limit of the speed.  The users
agreed and later reported a huge win from the adoption of DAMON_RECLAIM on
their products.

It is Not a Bug but a Feature; But...
=====================================

So nothing is broken.  DAMOS quota is working as intended, as the upper
limit of the speed.  It also provides its behavior observability via DAMOS
stat.  In the real world production environment that runs long term active
workloads and matters stability, the speed sometimes being slow is not a
real problem.

But, the non-deterministic behavior is sometimes annoying, especially in
lab environments.  Even in a realistic production environment, when there
is a huge amount of DAMOS action unapplicable memory, the speed could be
problematically slow.  Let's suppose a virtual machines provider that
setup 99% of the host memory as hugetlb pages that cannot be reclaimed, to
give it to virtual machines.  Also, when aim-oriented DAMOS auto-tuning is
applied, this could also make the internal feedback loop confused.

The intention of the current behavior was that trying DAMOS action to
regions would anyway impose some overhead, and therefore somehow be
charged.  But in the real world, the overhead for failed action is much
lighter than successful action.  Charging those at the same ratio may be
unfair, or at least suboptimum in some environments.

DAMOS Action Failed Region Quota Charge Ratio
=============================================

Let users set the charge ratio for the action-failed memory, for more
optimal and deterministic use of DAMOS.  It allows users to specify the
numerator and the denominator of the ratio for flexible setup.  For
example, let's suppose the numerator and the denominator are set to 1 and
4,096, respectively.  The ratio is 1 / 4,096.  A DAMOS scheme action is
applied to 5 GiB memory.  For 1 GiB of the memory, the action is
succeeded.  For the rest (4 GiB), the action is failed.  Then, only 1 GiB
and 1 MiB quota is charged.

The optimal charge ratio will depend on the use case and system/workload. 
I'd recommend starting from setting the nominator as 1 and the denominator
as PAGE_SIZE and tune based on the results, because many DAMOS actions are
applied at page level.

Tests
=====

I tested this feature in the steps below.

1. Allocate 50% of system memory and mlock() it using a test program.
2. Fill up the page cache to exhaust nearly all free memory.
3. Start DAMON-based proactive reclamation with 100 MiB/second DAMOS
   hard-quota.  Auto-tune the DAMOS soft-quota under the hard-quota for
   achieving 40% free memory of the system with 'temporal' tuner.

For step 1, I run a simple C program that is written by Gemini.  It is
quite straightforward, so I'm not sharing the code here.

For step 2, I use dd command like below:

   dd if=/dev/zero of=foo bs=1M count=$50_percent_of_system_memory

For step 3, I use the latest version of DAMON user-space tool (damo) like
below.

    sudo damo start --damos_action pageout \
            ` # Do the pageout only up to 100 MiB per second ` \
            --damos_quota_space 100M --damos_quota_interval 1s \
            ` # Auto-tune the quota below the hard quota aiming` \
            ` # 40% free memory of the node 0 ` \
            ` # (entire node of the test system)` \
            --damos_quota_goal node_mem_free_bp 40% 0 \
            ` # use temporal tuner, which is easy to understnd ` \
            --damos_quota_goal_tuner temporal

As expected, the progress of the reclamation is not consistent, because
the quota is exceeded for the failed reclamation of the unreclaimable
memory.

I do this again, but with the failed region charge ratio feature.  For
this, the above 'damo' command is used, after appending command line
option for setup of the charge ratio like below.  Note that the option was
added to 'damo' after v3.1.9.

    sudo ./damo start --damos_action pageout \
            [...]
            ` # quota-charge only 1/4096 for pageout-failed regions ` \
            --damos_quota_fail_charge_ratio 1 4096

The progress of the reclamation was nearly 100 MiB per second until the
goal was achieved, meeting the expectation.

Patches Sequence
================

The first two patches make preparational changes.  Patch 1 updates fully
charged quota check to handle <min_region_sz remaining quota, which will
be able to exist after this series is applied.  Patch 2 merges regions
after applying schemes is done as long as it is ok to do, since regions
split operations for quota could happen much more frequently under a
corner case that this series will make available.

Patch 3 implements the feature and exposes it via DAMON core API.  Patch 4
implements DAMON sysfs ABI for the feature.  Three following patches (5-7)
document the feature and ABI on design, usage, and ABI documents,
respectively.  Four patches for testing of the new feature follow.  Patch
8 implements a kunit test for the feature.  Patches 9 and 10 extend DAMON
selftest helpers for DAMON sysfs control and internal state dumping for
adding a new selftest for the feature.  Patch 11 extends existing DAMON
sysfs interface selftest to test the new feature using the extended helper
scripts.


This patch (of 11):

Less than min_region_sz remaining quota effectively means the quota is
fully charged.  In other words, no remaining quota.  This is because DAMOS
actions are applied in the region granularity, and each region should have
min_region_sz or larger size.  However the existing fully charged quota
check, which is also used for setting charge_target_from and
charge_addr_from of the quota, is not aware of the case.  For the reason,
charge_target_from and charge_addr_from of the quota will not be updated
in the case.  This can result in DAMOS action being applied more
frequently to a specific area of the memory.

The case is unreal because quota charging is also made in the region
granularity.  It could be changed in future, though.  Actually, the
following commit will make the change, by allowing users to set arbitrary
quota charging ratio for action-failed regions.  To be prepared for the
change, update the fully charged quota checks to treat having less than
min_region_sz remaining quota as fully charged.

Link: https://lore.kernel.org/20260428013402.115171-1-sj@kernel.org
Link: https://lore.kernel.org/20260428013402.115171-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:04:42 -07:00
Ravi Jonnalagadda
9138e27a3b mm/damon: add node_eligible_mem_bp goal metric 
Background and Motivation
=========================

In heterogeneous memory systems, controlling memory distribution across
NUMA nodes is essential for performance optimization.  This patch enables
system-wide page distribution with target-state goals such as "maintain
60% of scheme-eligible memory on DRAM" using PA-mode DAMON schemes.

Rather than using absolute thresholds, this metric tracks the ratio of
memory that matches each scheme's access pattern filters on a target node,
enabling the quota system to automatically adjust migration aggressiveness
to maintain the desired distribution.

What This Metric Measures
=========================

node_eligible_mem_bp:
    scheme_eligible_bytes_on_node / total_scheme_eligible_bytes * 10000

Two-Scheme Setup for Hot Page Distribution
==========================================

For maintaining 60% of hot memory on DRAM (node 0) and 40% on CXL
(node 1):

    PULL scheme: migrate_hot to node 0
      goal: node_eligible_mem_bp, nid=0, target=6000
      addr filter: node 1 address range (only migrate FROM CXL)
      "Move hot pages to DRAM if less than 60% of hot data is in DRAM"

    PUSH scheme: migrate_hot to node 1
      goal: node_eligible_mem_bp, nid=1, target=4000
      addr filter: node 0 address range (only migrate FROM DRAM)
      "Move hot pages to CXL if less than 40% of hot data is in CXL"

Each scheme independently measures its own eligible memory and adjusts its
quota to achieve its target ratio.  The schemes work in concert through
DAMON's unified monitoring context, with the quota autotuner balancing
their relative aggressiveness.

Implementation Details
======================

The implementation adds a new quota goal metric type
DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP to the existing DAMOS quota goal
framework.  When this metric is configured for a scheme:

1. During each quota adjustment cycle, damos_get_node_eligible_mem_bp()
   is called to calculate the current memory distribution.

2. The function iterates through all regions that match the scheme's
   access pattern (via __damos_valid_target()) and calculates:
   - Total eligible bytes across all nodes
   - Eligible bytes specifically on the target node (goal->nid)

3. For each eligible region, damos_calc_eligible_bytes() walks through
   the physical address range, using damon_get_folio() to look up
   each folio and determine its NUMA node via folio_nid().

4. Large folios are handled by calculating the exact overlap between
   the region boundaries and folio boundaries, ensuring accurate
   byte counts even when regions partially span folios.

5. The ratio (node_eligible / total_eligible * 10000) is returned
   as basis points, which the quota autotuner uses to adjust the
   scheme's effective quota size (esz).

The implementation requires CONFIG_DAMON_PADDR since damon_get_folio()
is only available for physical address space monitoring.

Testing Results
===============

Functionally tested on a two-node heterogeneous memory system with DRAM
(node 0) and CXL memory (node 1).  A PUSH+PULL scheme configuration using
migrate_hot actions was used to reach a target hot memory ratio between
the two tiers.

With the TEMPORAL tuner, the system converges quickly to the target
distribution.  The tuner drives esz to maximum when under goal and to zero
once the goal is met, forming a simple on/off feedback loop that
stabilizes at the desired ratio.

With the CONSIST tuner, the scheme still converges but more slowly, as it
migrates and then throttles itself based on quota feedback.  The time to
reach the goal varies depending on workload intensity.

Note: This metric works with both TEMPORAL and CONSIST goal tuners.

Link: https://lore.kernel.org/20260428030520.701-1-ravis.opensrc@gmail.com
Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@gmail.com>
Suggested-by: SeongJae Park <sj@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Honggyu Kim <honggyu.kim@sk.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Yunjeong Mun <yunjeong.mun@sk.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:04:42 -07:00
SeongJae Park
5a2d162e22 mm/damon/core: make charge_addr_from aware of end-address exclusivity 
DAMON region end address is exclusive one, but charge_addr_from is
assigned assuming the end address is inclusive.  As a result, DAMOS action
to next up to min_region_sz memory can be skipped.  This is quite
negligible user impact.  But, the bug is a bug that can be very simply
fixed.  Fix the wrong assignment to respect the exclusiveness of the
address.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260428042942.118230-1-sj@kernel.org
Link: https://lore.kernel.org/20260428032324.115663-1-sj@kernel.org [1]
Fixes: 50585192bc ("mm/damon/schemes: skip already charged targets and regions")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:04:41 -07:00
Linus Torvalds
c1f49dea2b 7 hotfixes. 6 are cc:stable and all are for MM. Please see the 
individual changelogs for details.
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Merge tag 'mm-hotfixes-stable-2026-04-19-00-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM fixes from Andrew Morton:
 "7 hotfixes. 6 are cc:stable and all are for MM. Please see the
  individual changelogs for details"

* tag 'mm-hotfixes-stable-2026-04-19-00-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm:
  mm/damon/core: disallow non-power of two min_region_sz on damon_start()
  mm/vmalloc: take vmap_purge_lock in shrinker
  mm: call ->free_folio() directly in folio_unmap_invalidate()
  mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()
  mm/zone_device: do not touch device folio after calling ->folio_free()
  mm/damon/core: disallow time-quota setting zero esz
  mm/mempolicy: fix weighted interleave auto sysfs name
 2026-04-19 14:45:37 -07:00
Linus Torvalds
40735a683b mm.git review status for linus..mm-stable 
Everything:
 
 Total patches:       121
 Reviews/patch:       2.11
 Reviewed rate:       90%
 
 Excluding DAMON:
 
 Total patches:       113
 Reviews/patch:       2.25
 Reviewed rate:       96%
 
 - The 33 patch series "Eliminate Dying Memory Cgroup" from Qi Zheng and
   Muchun Song addresses the longstanding "dying memcg problem".  A
   situation wherein a no-longer-used memory control group will hang around
   for an extended period pointlessly consuming memory.  The [0/N]
   changelog has a good overview of this work.
 
 - The 3 patch series "fix unexpected type conversions and potential
   overflows" from Qi Zheng fixes a couple of potential 32-bit/64-bit
   issues which were identified during review of the "Eliminate Dying
   Memory Cgroup" series.
 
 - The 6 patch series "kho: history: track previous kernel version and
   kexec boot count" from Breno Leitao uses Kexec Handover (KHO) to pass
   the previous kernel's version string and the number of kexec reboots
   since the last cold boot to the next kernel, and prints it at boot time.
 
 - The 4 patch series "liveupdate: prevent double preservation" from
   Pasha Tatashin teaches LUO to avoid managing the same file across
   different active sessions.
 
 - The 10 patch series "liveupdate: Fix module unloading and unregister
   API" from Pasha Tatashin addresses an issue with how LUO handles module
   reference counting and unregistration during module unloading.
 
 - The 2 patch series "zswap pool per-CPU acomp_ctx simplifications" from
   Kanchana Sridhar simplifies and cleans up the zswap crypto compression
   handling and improves the lifecycle management of zswap pool's per-CPU
   acomp_ctx resources.
 
 - The 2 patch series "mm/damon/core: fix damon_call()/damos_walk() vs
   kdmond exit race" from SeongJae Park addresses unlikely but possible
   leaks and deadlocks in damon_call() and damon_walk().
 
 - The 2 patch series "mm/damon/core: validate damos_quota_goal->nid"
   from SeongJae Park fixes a couple of root-only wild pointer
   dereferences.
 
 - The 2 patch series "Docs/admin-guide/mm/damon: warn commit_inputs vs
   other params race" from SeongJae Park updates the DAMON documentation to
   warn operators about potential races which can occur if the
   commit_inputs parameter is altered at the wrong time.
 
 - The 3 patch series "Minor hmm_test fixes and cleanups" from Alistair
   Popple implements two bugfixes a cleanup for the HMM kernel selftests.
 
 - The 6 patch series "Modify memfd_luo code" from Chenghao Duan provides
   cleanups, simplifications and speedups in the memfd_lou code.
 
 - The 4 patch series "mm, kvm: allow uffd support in guest_memfd" from
   Mike Rapoport enables support for userfaultfd in guest_memfd.
 
 - The 6 patch series "selftests/mm: skip several tests when thp is not
   available" from Chunyu Hu fixes several issues in the selftests code
   which were causing breakage when the tests were run on CONFIG_THP=n
   kernels.
 
 - The 2 patch series "mm/mprotect: micro-optimization work" from Pedro
   Falcato implements a couple of nice speedups for mprotect().
 
 - The 3 patch series "MAINTAINERS: update KHO and LIVE UPDATE entries"
   from Pratyush Yadav reflects upcoming changes in the maintenance of KHO,
   LUO, memfd_luo, kexec, crash, kdump and probably other kexec-based
   things - they are being moved out of mm.git and into a new git tree.
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Merge tag 'mm-stable-2026-04-18-02-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull more MM updates from Andrew Morton:

 - "Eliminate Dying Memory Cgroup" (Qi Zheng and Muchun Song)

   Address the longstanding "dying memcg problem". A situation wherein a
   no-longer-used memory control group will hang around for an extended
   period pointlessly consuming memory

 - "fix unexpected type conversions and potential overflows" (Qi Zheng)

   Fix a couple of potential 32-bit/64-bit issues which were identified
   during review of the "Eliminate Dying Memory Cgroup" series

 - "kho: history: track previous kernel version and kexec boot count"
   (Breno Leitao)

   Use Kexec Handover (KHO) to pass the previous kernel's version string
   and the number of kexec reboots since the last cold boot to the next
   kernel, and print it at boot time

 - "liveupdate: prevent double preservation" (Pasha Tatashin)

   Teach LUO to avoid managing the same file across different active
   sessions

 - "liveupdate: Fix module unloading and unregister API" (Pasha
   Tatashin)

   Address an issue with how LUO handles module reference counting and
   unregistration during module unloading

 - "zswap pool per-CPU acomp_ctx simplifications" (Kanchana Sridhar)

   Simplify and clean up the zswap crypto compression handling and
   improve the lifecycle management of zswap pool's per-CPU acomp_ctx
   resources

 - "mm/damon/core: fix damon_call()/damos_walk() vs kdmond exit race"
   (SeongJae Park)

   Address unlikely but possible leaks and deadlocks in damon_call() and
   damon_walk()

 - "mm/damon/core: validate damos_quota_goal->nid" (SeongJae Park)

   Fix a couple of root-only wild pointer dereferences

 - "Docs/admin-guide/mm/damon: warn commit_inputs vs other params race"
   (SeongJae Park)

   Update the DAMON documentation to warn operators about potential
   races which can occur if the commit_inputs parameter is altered at
   the wrong time

 - "Minor hmm_test fixes and cleanups" (Alistair Popple)

   Bugfixes and a cleanup for the HMM kernel selftests

 - "Modify memfd_luo code" (Chenghao Duan)

   Cleanups, simplifications and speedups to the memfd_lou code

 - "mm, kvm: allow uffd support in guest_memfd" (Mike Rapoport)

   Support for userfaultfd in guest_memfd

 - "selftests/mm: skip several tests when thp is not available" (Chunyu
   Hu)

   Fix several issues in the selftests code which were causing breakage
   when the tests were run on CONFIG_THP=n kernels

 - "mm/mprotect: micro-optimization work" (Pedro Falcato)

   A couple of nice speedups for mprotect()

 - "MAINTAINERS: update KHO and LIVE UPDATE entries" (Pratyush Yadav)

   Document upcoming changes in the maintenance of KHO, LUO, memfd_luo,
   kexec, crash, kdump and probably other kexec-based things - they are
   being moved out of mm.git and into a new git tree

* tag 'mm-stable-2026-04-18-02-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (121 commits)
  MAINTAINERS: add page cache reviewer
  mm/vmscan: avoid false-positive -Wuninitialized warning
  MAINTAINERS: update Dave's kdump reviewer email address
  MAINTAINERS: drop include/linux/liveupdate from LIVE UPDATE
  MAINTAINERS: drop include/linux/kho/abi/ from KHO
  MAINTAINERS: update KHO and LIVE UPDATE maintainers
  MAINTAINERS: update kexec/kdump maintainers entries
  mm/migrate_device: remove dead migration entry check in migrate_vma_collect_huge_pmd()
  selftests: mm: skip charge_reserved_hugetlb without killall
  userfaultfd: allow registration of ranges below mmap_min_addr
  mm/vmstat: fix vmstat_shepherd double-scheduling vmstat_update
  mm/hugetlb: fix early boot crash on parameters without '=' separator
  zram: reject unrecognized type= values in recompress_store()
  docs: proc: document ProtectionKey in smaps
  mm/mprotect: special-case small folios when applying permissions
  mm/mprotect: move softleaf code out of the main function
  mm: remove '!root_reclaim' checking in should_abort_scan()
  mm/sparse: fix comment for section map alignment
  mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete()
  selftests/mm: transhuge_stress: skip the test when thp not available
  ...
 2026-04-19 08:01:17 -07:00
SeongJae Park
95093e5cb4 mm/damon/core: disallow non-power of two min_region_sz on damon_start() 
Commit d8f867fa08 ("mm/damon: add damon_ctx->min_sz_region") introduced
a bug that allows unaligned DAMON region address ranges.  Commit
c80f46ac22 ("mm/damon/core: disallow non-power of two min_region_sz")
fixed it, but only for damon_commit_ctx() use case.  Still, DAMON sysfs
interface can emit non-power of two min_region_sz via damon_start().  Fix
the path by adding the is_power_of_2() check on damon_start().

The issue was discovered by sashiko [1].

Link: https://lore.kernel.org/20260411213638.77768-1-sj@kernel.org
Link: https://lore.kernel.org/20260403155530.64647-1-sj@kernel.org [1]
Fixes: d8f867fa08 ("mm/damon: add damon_ctx->min_sz_region")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 23:24:27 -07:00
SeongJae Park
8bbde987c2 mm/damon/core: disallow time-quota setting zero esz 
When the throughput of a DAMOS scheme is very slow, DAMOS time quota can
make the effective size quota smaller than damon_ctx->min_region_sz.  In
the case, damos_apply_scheme() will skip applying the action, because the
action is tried at region level, which requires >=min_region_sz size. 
That is, the quota is effectively exceeded for the quota charge window.

Because no action will be applied, the total_charged_sz and
total_charged_ns are also not updated.  damos_set_effective_quota() will
try to update the effective size quota before starting the next charge
window.  However, because the total_charged_sz and total_charged_ns have
not updated, the throughput and effective size quota are also not changed.
Since effective size quota can only be decreased, other effective size
quota update factors including DAMOS quota goals and size quota cannot
make any change, either.

As a result, the scheme is unexpectedly deactivated until the user notices
and mitigates the situation.  The users can mitigate this situation by
changing the time quota online or re-install the scheme.  While the
mitigation is somewhat straightforward, finding the situation would be
challenging, because DAMON is not providing good observabilities for that.
Even if such observability is provided, doing the additional monitoring
and the mitigation is somewhat cumbersome and not aligned to the intention
of the time quota.  The time quota was intended to help reduce the user's
administration overhead.

Fix the problem by setting time quota-modified effective size quota be at
least min_region_sz always.

The issue was discovered [1] by sashiko.

Link: https://lore.kernel.org/20260407003153.79589-1-sj@kernel.org
Link: https://lore.kernel.org/20260405192504.110014-1-sj@kernel.org [1]
Fixes: 1cd2430300 ("mm/damon/schemes: implement time quota")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 23:24:27 -07:00
SeongJae Park
049a57421d mm/damon/core: use time_in_range_open() for damos quota window start 
damos_adjust_quota() uses time_after_eq() to show if it is time to start a
new quota charge window, comparing the current jiffies and the scheduled
next charge window start time.  If it is, the next charge window start
time is updated and the new charge window starts.

The time check and next window start time update is skipped while the
scheme is deactivated by the watermarks.  Let's suppose the deactivation
is kept more than LONG_MAX jiffies (assuming CONFIG_HZ of 250, more than
99 days in 32 bit systems and more than one billion years in 64 bit
systems), resulting in having the jiffies larger than the next charge
window start time + LONG_MAX.  Then, the time_after_eq() call can return
false until another LONG_MAX jiffies are passed.

This means the scheme can continue working after being reactivated by the
watermarks.  But, soon, the quota will be exceeded and the scheme will
again effectively stop working until the next charge window starts. 
Because the current charge window is extended to up to LONG_MAX jiffies,
however, it will look like it stopped unexpectedly and indefinitely, from
the user's perspective.

Fix this by using !time_in_range_open() instead.

The issue was discovered [1] by sashiko.

Link: https://lore.kernel.org/20260329152306.45796-1-sj@kernel.org
Link: https://lore.kernel.org/20260324040722.57944-1-sj@kernel.org [1]
Fixes: ee801b7dd7 ("mm/damon/schemes: activate schemes based on a watermarks mechanism")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 00:10:51 -07:00
SeongJae Park
a34dac6482 mm/damon/core: validate damos_quota_goal->nid for node_memcg_{used,free}_bp 
Users can set damos_quota_goal->nid with arbitrary value for
node_memcg_{used,free}_bp.  But DAMON core is using those for NODE-DATA()
without a validation of the value.  This can result in out of bounds
memory access.  The issue can actually triggered using DAMON user-space
tool (damo), like below.

    $ sudo mkdir /sys/fs/cgroup/foo
    $ sudo ./damo start --damos_action stat --damos_quota_interval 1s \
            --damos_quota_goal node_memcg_used_bp 50% -1 /foo
    $ sudo dmseg
    [...]
    [  524.181426] Unable to handle kernel paging request at virtual address 0000000000002c00

Fix this issue by adding the validation of the given node id.  If an
invalid node id is given, it returns 0% for used memory ratio, and 100%
for free memory ratio.

Link: https://lore.kernel.org/20260329043902.46163-3-sj@kernel.org
Fixes: b74a120bcf ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.19.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 00:10:51 -07:00
SeongJae Park
40250b2dde mm/damon/core: validate damos_quota_goal->nid for node_mem_{used,free}_bp 
Patch series "mm/damon/core: validate damos_quota_goal->nid".

node_mem[cg]_{used,free}_bp DAMOS quota goals receive the node id.  The
node id is used for si_meminfo_node() and NODE_DATA() without proper
validation.  As a result, privileged users can trigger an out of bounds
memory access using DAMON_SYSFS.  Fix the issues.

The issue was originally reported [1] with a fix by another author.  The
original author announced [2] that they will stop working including the
fix that was still in the review stage.  Hence I'm restarting this.


This patch (of 2):

Users can set damos_quota_goal->nid with arbitrary value for
node_mem_{used,free}_bp.  But DAMON core is using those for
si_meminfo_node() without the validation of the value.  This can result in
out of bounds memory access.  The issue can actually triggered using DAMON
user-space tool (damo), like below.

    $ sudo ./damo start --damos_action stat \
    	--damos_quota_goal node_mem_used_bp 50% -1 \
    	--damos_quota_interval 1s
    $ sudo dmesg
    [...]
    [   65.565986] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000098

Fix this issue by adding the validation of the given node.  If an invalid
node id is given, it returns 0% for used memory ratio, and 100% for free
memory ratio.

Link: https://lore.kernel.org/20260329043902.46163-2-sj@kernel.org
Link: https://lore.kernel.org/20260325073034.140353-1-objecting@objecting.org [1]
Link: https://lore.kernel.org/20260327040924.68553-1-sj@kernel.org [2]
Fixes: 0e1c773b50 ("mm/damon/core: introduce damos quota goal metrics for memory node utilization")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 00:10:51 -07:00
SeongJae Park
33c3f6c2b4 mm/damon/core: fix damos_walk() vs kdamond_fn() exit race 
When kdamond_fn() main loop is finished, the function cancels remaining
damos_walk() request and unset the damon_ctx->kdamond so that API callers
and API functions themselves can show the context is terminated. 
damos_walk() adds the caller's request to the queue first.  After that, it
shows if the kdamond of the damon_ctx is still running (damon_ctx->kdamond
is set).  Only if the kdamond is running, damos_walk() starts waiting for
the kdamond's handling of the newly added request.

The damos_walk() requests registration and damon_ctx->kdamond unset are
protected by different mutexes, though.  Hence, damos_walk() could race
with damon_ctx->kdamond unset, and result in deadlocks.

For example, let's suppose kdamond successfully finished the damow_walk()
request cancelling.  Right after that, damos_walk() is called for the
context.  It registers the new request, and shows the context is still
running, because damon_ctx->kdamond unset is not yet done.  Hence the
damos_walk() caller starts waiting for the handling of the request. 
However, the kdamond is already on the termination steps, so it never
handles the new request.  As a result, the damos_walk() caller thread
infinitely waits.

Fix this by introducing another damon_ctx field, namely
walk_control_obsolete.  It is protected by the
damon_ctx->walk_control_lock, which protects damos_walk() request
registration.  Initialize (unset) it in kdamond_fn() before letting
damon_start() returns and set it just before the cancelling of the
remaining damos_walk() request is executed.  damos_walk() reads the
obsolete field under the lock and avoids adding a new request.

After this change, only requests that are guaranteed to be handled or
cancelled are registered.  Hence the after-registration DAMON context
termination check is no longer needed.  Remove it together.

The issue is found by sashiko [1].


Link: https://lore.kernel.org/20260327233319.3528-3-sj@kernel.org
Link: https://lore.kernel.org/20260325141956.87144-1-sj@kernel.org [1]
Fixes: bf0eaba0ff ("mm/damon/core: implement damos_walk()")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.14.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 00:10:51 -07:00
SeongJae Park
55da81663b mm/damon/core: fix damon_call() vs kdamond_fn() exit race 
Patch series "mm/damon/core: fix damon_call()/damos_walk() vs kdmond exit
race".

damon_call() and damos_walk() can leak memory and/or deadlock when they
race with kdamond terminations.  Fix those.


This patch (of 2);

When kdamond_fn() main loop is finished, the function cancels all
remaining damon_call() requests and unset the damon_ctx->kdamond so that
API callers and API functions themselves can know the context is
terminated.  damon_call() adds the caller's request to the queue first. 
After that, it shows if the kdamond of the damon_ctx is still running
(damon_ctx->kdamond is set).  Only if the kdamond is running, damon_call()
starts waiting for the kdamond's handling of the newly added request.

The damon_call() requests registration and damon_ctx->kdamond unset are
protected by different mutexes, though.  Hence, damon_call() could race
with damon_ctx->kdamond unset, and result in deadlocks.

For example, let's suppose kdamond successfully finished the damon_call()
requests cancelling.  Right after that, damon_call() is called for the
context.  It registers the new request, and shows the context is still
running, because damon_ctx->kdamond unset is not yet done.  Hence the
damon_call() caller starts waiting for the handling of the request. 
However, the kdamond is already on the termination steps, so it never
handles the new request.  As a result, the damon_call() caller threads
infinitely waits.

Fix this by introducing another damon_ctx field, namely
call_controls_obsolete.  It is protected by the
damon_ctx->call_controls_lock, which protects damon_call() requests
registration.  Initialize (unset) it in kdamond_fn() before letting
damon_start() returns and set it just before the cancelling of remaining
damon_call() requests is executed.  damon_call() reads the obsolete field
under the lock and avoids adding a new request.

After this change, only requests that are guaranteed to be handled or
cancelled are registered.  Hence the after-registration DAMON context
termination check is no longer needed.  Remove it together.

Note that the deadlock will not happen when damon_call() is called for
repeat mode request.  In tis case, damon_call() returns instead of waiting
for the handling when the request registration succeeds and it shows the
kdamond is running.  However, if the request also has dealloc_on_cancel,
the request memory would be leaked.

The issue is found by sashiko [1].

Link: https://lore.kernel.org/20260327233319.3528-1-sj@kernel.org
Link: https://lore.kernel.org/20260327233319.3528-2-sj@kernel.org
Link: https://lore.kernel.org/20260325141956.87144-1-sj@kernel.org [1]
Fixes: 42b7491af1 ("mm/damon/core: introduce damon_call()")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.14.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 00:10:51 -07:00
Linus Torvalds
cb30bf881c tracing updates for v7.1: 
- Fix printf format warning for bprintf
 
   sunrpc uses a trace_printk() that triggers a printf warning during the
   compile. Move the __printf() attribute around for when debugging is not
   enabled the warning will go away.
 
 - Remove redundant check for EVENT_FILE_FL_FREED in event_filter_write()
 
   The FREED flag is checked in the call to event_file_file() and then
   checked again right afterward, which is unneeded.
 
 - Clean up event_file_file() and event_file_data() helpers
 
   These helper functions played a different role in the past, but now with
   eventfs, the READ_ONCE() isn't needed. Simplify the code a bit and also
   add a warning to event_file_data() if the file or its data is not present.
 
 - Remove updating file->private_data in tracing open
 
   All access to the file private data is handled by the helper functions,
   which do not use file->private_data. Stop updating it on open.
 
 - Show ENUM names in function arguments via BTF in function tracing
 
   When showing the function arguments when func-args option is set for
   function tracing, if one of the arguments is found to be an enum, show the
   name of the enum instead of its number.
 
 - Add new trace_call__##name() API for tracepoints
 
   Tracepoints are enabled via static_branch() blocks, where when not
   enabled, there's only a nop that is in the code where the execution will
   just skip over it. When tracing is enabled, the nop is converted to a
   direct jump to the tracepoint code. Sometimes more calculations are
   required to be performed to update the parameters of the tracepoint. In
   this case, trace_##name##_enabled() is called which is a static_branch()
   that gets enabled only when the tracepoint is enabled. This allows the
   extra calculations to also be skipped by the nop:
 
   if (trace_foo_enabled()) {
       x = bar();
       trace_foo(x);
   }
 
   Where the x=bar() is only performed when foo is enabled. The problem with
   this approach is that there's now two static_branch() calls. One for
   checking if the tracepoint is enabled, and then again to know if the
   tracepoint should be called. The second one is redundant.
 
   Introduce trace_call__foo() that will call the foo() tracepoint directly
   without doing a static_branch():
 
   if (trace_foo_enabled()) {
       x = bar();
       trace_call__foo();
   }
 
 - Update various locations to use the new trace_call__##name() API
 
 - Move snapshot code out of trace.c
 
   Cleaning up trace.c to not be a "dump all", move the snapshot code out of
   it and into a new trace_snapshot.c file.
 
 - Clean up some "%*.s" to "%*s"
 
 - Allow boot kernel command line options to be called multiple times
 
   Have options like:
 
     ftrace_filter=foo ftrace_filter=bar ftrace_filter=zoo
 
   Equal to:
 
     ftrace_filter=foo,bar,zoo
 
 - Fix ipi_raise event CPU field to be a CPU field
 
   The ipi_raise target_cpus field is defined as a __bitmask(). There is now a
   __cpumask() field definition. Update the field to use that.
 
 - Have hist_field_name() use a snprintf() and not a series of strcat()
 
   It's safer to use snprintf() that a series of strcat().
 
 - Fix tracepoint regfunc balancing
 
   A tracepoint can define a "reg" and "unreg" function that gets called
   before the tracepoint is enabled, and after it is disabled respectively.
   But on error, after the "reg" func is called and the tracepoint is not
   enabled, the "unreg" function is not called to tear down what the "reg"
   function performed.
 
 - Fix output that shows what histograms are enabled
 
   Event variables are displayed incorrectly in the histogram output.
 
   Instead of "sched.sched_wakeup.$var", it is showing
   "$sched.sched_wakeup.var" where the '$' is in the incorrect location.
 
 - Some other simple cleanups.
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Merge tag 'trace-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing updates from Steven Rostedt:

 - Fix printf format warning for bprintf

   sunrpc uses a trace_printk() that triggers a printf warning during
   the compile. Move the __printf() attribute around for when debugging
   is not enabled the warning will go away

 - Remove redundant check for EVENT_FILE_FL_FREED in
   event_filter_write()

   The FREED flag is checked in the call to event_file_file() and then
   checked again right afterward, which is unneeded

 - Clean up event_file_file() and event_file_data() helpers

   These helper functions played a different role in the past, but now
   with eventfs, the READ_ONCE() isn't needed. Simplify the code a bit
   and also add a warning to event_file_data() if the file or its data
   is not present

 - Remove updating file->private_data in tracing open

   All access to the file private data is handled by the helper
   functions, which do not use file->private_data. Stop updating it on
   open

 - Show ENUM names in function arguments via BTF in function tracing

   When showing the function arguments when func-args option is set for
   function tracing, if one of the arguments is found to be an enum,
   show the name of the enum instead of its number

 - Add new trace_call__##name() API for tracepoints

   Tracepoints are enabled via static_branch() blocks, where when not
   enabled, there's only a nop that is in the code where the execution
   will just skip over it. When tracing is enabled, the nop is converted
   to a direct jump to the tracepoint code. Sometimes more calculations
   are required to be performed to update the parameters of the
   tracepoint. In this case, trace_##name##_enabled() is called which is
   a static_branch() that gets enabled only when the tracepoint is
   enabled. This allows the extra calculations to also be skipped by the
   nop:

	if (trace_foo_enabled()) {
		x = bar();
		trace_foo(x);
	}

   Where the x=bar() is only performed when foo is enabled. The problem
   with this approach is that there's now two static_branch() calls. One
   for checking if the tracepoint is enabled, and then again to know if
   the tracepoint should be called. The second one is redundant

   Introduce trace_call__foo() that will call the foo() tracepoint
   directly without doing a static_branch():

	if (trace_foo_enabled()) {
		x = bar();
		trace_call__foo();
	}

 - Update various locations to use the new trace_call__##name() API

 - Move snapshot code out of trace.c

   Cleaning up trace.c to not be a "dump all", move the snapshot code
   out of it and into a new trace_snapshot.c file

 - Clean up some "%*.s" to "%*s"

 - Allow boot kernel command line options to be called multiple times

   Have options like:

	ftrace_filter=foo ftrace_filter=bar ftrace_filter=zoo

   Equal to:

	ftrace_filter=foo,bar,zoo

 - Fix ipi_raise event CPU field to be a CPU field

   The ipi_raise target_cpus field is defined as a __bitmask(). There is
   now a __cpumask() field definition. Update the field to use that

 - Have hist_field_name() use a snprintf() and not a series of strcat()

   It's safer to use snprintf() that a series of strcat()

 - Fix tracepoint regfunc balancing

   A tracepoint can define a "reg" and "unreg" function that gets called
   before the tracepoint is enabled, and after it is disabled
   respectively. But on error, after the "reg" func is called and the
   tracepoint is not enabled, the "unreg" function is not called to tear
   down what the "reg" function performed

 - Fix output that shows what histograms are enabled

   Event variables are displayed incorrectly in the histogram output

   Instead of "sched.sched_wakeup.$var", it is showing
   "$sched.sched_wakeup.var" where the '$' is in the incorrect location

 - Some other simple cleanups

* tag 'trace-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (24 commits)
  selftests/ftrace: Add test case for fully-qualified variable references
  tracing: Fix fully-qualified variable reference printing in histograms
  tracepoint: balance regfunc() on func_add() failure in tracepoint_add_func()
  tracing: Rebuild full_name on each hist_field_name() call
  tracing: Report ipi_raise target CPUs as cpumask
  tracing: Remove duplicate latency_fsnotify() stub
  tracing: Preserve repeated trace_trigger boot parameters
  tracing: Append repeated boot-time tracing parameters
  tracing: Remove spurious default precision from show_event_trigger/filter formats
  cpufreq: Use trace_call__##name() at guarded tracepoint call sites
  tracing: Remove tracing_alloc_snapshot() when snapshot isn't defined
  tracing: Move snapshot code out of trace.c and into trace_snapshot.c
  mm: damon: Use trace_call__##name() at guarded tracepoint call sites
  btrfs: Use trace_call__##name() at guarded tracepoint call sites
  spi: Use trace_call__##name() at guarded tracepoint call sites
  i2c: Use trace_call__##name() at guarded tracepoint call sites
  kernel: Use trace_call__##name() at guarded tracepoint call sites
  tracepoint: Add trace_call__##name() API
  tracing: trace_mmap.h: fix a kernel-doc warning
  tracing: Pretty-print enum parameters in function arguments
  ...
 2026-04-17 09:43:12 -07:00
Josh Law
cc4555fc6d mm/damon/core: document damos_commit_dests() failure semantics 
Add a kernel-doc-like comment to damos_commit_dests() documenting its
allocation failure contract: on -ENOMEM, the destination structure is left
in a partially torn-down state that is safe to deallocate via
damon_destroy_scheme(), but must not be reused for further commits.

This was unclear from the code alone and led to a separate patch [1]
attempting to reset nr_dests on failure.  Make the intended usage explicit
so future readers do not repeat the confusion.

Link: https://lkml.kernel.org/r/20260320143648.91673-1-sj@kernel.org
Link: https://lore.kernel.org/20260318214939.36100-1-objecting@objecting.org [1]
Signed-off-by: Josh Law <objecting@objecting.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:34 -07:00
SeongJae Park
5f9a5926b7 mm/damon/core: fix wrong damon_set_regions() argument 
The third argument is the length of the second parameter.  But addr_unit
is wrongly being passed.  Fix it.

Link: https://lkml.kernel.org/r/20260314001854.79623-1-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Yang yingliang <yangyingliang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:29 -07:00
SeongJae Park
eabc2eddb2 mm/damon/core: receive addr_unit on damon_set_region_biggest_system_ram_default() 
damon_find_biggest_system_ram() was not supporting addr_unit in the past. 
Hence, its caller, damon_set_region_biggest_system_ram_default(), was also
not supporting addr_unit.  The previous commit has updated the inner
function to support addr_unit.  There is no more reason to not support
addr_unit on damon_set_region_biggest_system_ram_default().  Rather, it
makes unnecessary inconsistency on support of addr_unit.  Update it to
receive addr_unit and handle it inside.

Link: https://lkml.kernel.org/r/20260311052927.93921-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Yang yingliang <yangyingliang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:28 -07:00
SeongJae Park
b47dcc1a28 mm/damon/core: support addr_unit on damon_find_biggest_system_ram() 
damon_find_biggest_system_ram() sets an 'unsigned long' variable with
'resource_size_t' value.  This is fundamentally wrong.  On environments
such as ARM 32 bit machines having LPAE (Large Physical Address
Extensions), which DAMON supports, the size of 'unsigned long' may be
smaller than that of 'resource_size_t'.  It is safe, though, since we
restrict the walk to be done only up to ULONG_MAX.

DAMON supports the address size gap using 'addr_unit'.  We didn't add the
support to the function, just to make the initial support change small. 
Now the support is reasonably settled.  This kind of gap is only making
the code inconsistent and easy to be confused.  Add the support of
'addr_unit' to the function, by letting callers pass the 'addr_unit' and
handling it in the function.  All callers are passing 'addr_unit' 1,
though, to keep the old behavior.

[sj@kernel.org: verify found biggest system ram]
  Link: https://lkml.kernel.org/r/20260317144725.88524-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20260311052927.93921-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Yang yingliang <yangyingliang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:28 -07:00
SeongJae Park
c63067e8b0 mm/damon/core: fix wrong end address assignment on walk_system_ram() 
Patch series "mm/damon: support addr_unit on default monitoring targets
for modules".

DAMON_RECLAIM and DAMON_LRU_SORT support 'addr_unit' parameters only when
the monitoring target address range is explicitly set.  This was
intentional for making the initial 'addr_unit' support change small.  Now
'addr_unit' support is being quite stabilized.  Having the corner case of
the support is only making the code inconsistent with implicit rules.  The
inconsistency makes it easy to confuse [1] readers.  After all, there is
no real reason to keep 'addr_unit' support incomplete.  Add the support
for the case to improve the readability and more completely support
'addr_unit'.

This series is constructed with five patches.  The first one (patch 1)
fixes a small bug that mistakenly assigns inclusive end address to open
end address, which was found from this work.  The second and third ones
(patches 2 and 3) extend the default monitoring target setting functions
in the core layer one by one, to support the 'addr_unit' while making no
visible changes.  The final two patches (patches 4 and 5) update
DAMON_RECLAIM and DAMON_LRU_SORT to support 'addr_unit' for the default
monitoring target address ranges, by passing the user input to the core
functions.


This patch (of 5):

'struct damon_addr_range' and 'struct resource' represent different types
of address ranges.  'damon_addr_range' is for end-open ranges ([start,
end)).  'resource' is for fully-closed ranges ([start, end]).  But
walk_system_ram() is assigning resource->end to damon_addr_range->end
without the inclusiveness adjustment.  As a result, the function returns
an address range that is missing the last one byte.

The function is being used to find and set the biggest system ram as the
default monitoring target for DAMON_RECLAIM and DAMON_LRU_SORT.  Missing
the last byte of the big range shouldn't be a real problem for the real
use cases.  That said, the loss is definitely an unintended behavior.  Do
the correct adjustment.

Link: https://lkml.kernel.org/r/20260311052927.93921-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20260311052927.93921-2-sj@kernel.org
Link: https://lore.kernel.org/20260131015643.79158-1-sj@kernel.org [1]
Fixes: 43b0536cb4 ("mm/damon: introduce DAMON-based Reclamation (DAMON_RECLAIM)")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Yang yingliang <yangyingliang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:28 -07:00
SeongJae Park
af738a6a00 mm/damon/core: introduce DAMOS_QUOTA_GOAL_TUNER_TEMPORAL 
Introduce a new goal-based DAMOS quota auto-tuning algorithm, namely
DAMOS_QUOTA_GOAL_TUNER_TEMPORAL (temporal in short).  The algorithm aims
to trigger the DAMOS action only for a temporal time, to achieve the goal
as soon as possible.  For the temporal period, it uses as much quota as
allowed.  Once the goal is achieved, it sets the quota zero, so
effectively makes the scheme be deactivated.

Link: https://lkml.kernel.org/r/20260310010529.91162-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:25 -07:00
SeongJae Park
54419bbd0e mm/damon/core: allow quota goals set zero effective size quota 
User-explicit quotas (size and time quotas) having zero value means the
quotas are unset.  And, effective size quota is set as the minimum value
of the explicit quotas.  When quota goals are set, the goal-based quota
tuner can make it lower.  But the existing only single tuner never sets
the effective size quota zero.  Because of the fact, DAMON core assumes
zero effective quota means the user has set no quota.

Multiple tuners are now allowed, though.  In the future, some tuners might
want to set a zero effective size quota.  There is no reason to restrict
that.  Meanwhile, because of the current implementation, it will only
deactivate all quotas and make the scheme work at its full speed.

Introduce a dedicated function for checking if no quota is set.  The
function checks the fact by showing if the user-set explicit quotas are
zero and no goal is installed.  It is decoupled from zero effective quota,
and hence allows future tuners set zero effective quota for intentionally
deactivating the scheme by a purpose.

Link: https://lkml.kernel.org/r/20260310010529.91162-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:25 -07:00
SeongJae Park
8719c59c4b mm/damon/core: introduce damos_quota_goal_tuner 
Patch series "mm/damon: support multiple goal-based quota tuning
algorithms".

Aim-oriented DAMOS quota auto-tuning uses a single tuning algorithm.  The
algorithm is designed to find a quota value that should be consistently
kept for achieving the aimed goal for long term.  It is useful and
reliable at automatically operating systems that have dynamic environments
in the long term.

As always, however, no single algorithm fits all.  When the environment
has static characteristics or there are control towers in not only the
kernel space but also the user space, the algorithm shows some
limitations.  In such environments, users want kernel work in a more short
term deterministic way.  Actually there were at least two reports [1,2] of
such cases.

Extend DAMOS quotas goal to support multiple quota tuning algorithms that
users can select.  Keep the current algorithm as the default one, to not
break the old users.  Also give it a name, "consist", as it is designed to
"consistently" apply the DAMOS action.  And introduce a new tuning
algorithm, namely "temporal".  It is designed to apply the DAMOS action
only temporally, in a deterministic way.  In more detail, as long as the
goal is under-achieved, it uses the maximum quota available.  Once the
goal is over-achieved, it sets the quota zero.

Tests
=====

I confirmed the feature is working as expected using the latest version of
DAMON user-space tool, like below.

    $ # start DAMOS for reclaiming memory aiming 30% free memory
    $ sudo ./damo/damo start --damos_action pageout \
            --damos_quota_goal_tuner temporal \
            --damos_quota_goal node_mem_free_bp 30% 0 \
            --damos_quota_interval 1s \
            --damos_quota_space 100M

Note that >=3.1.8 version of DAMON user-space tool supports this feature
(--damos_quota_goal_tuner).  As expected, DAMOS stops reclaiming memory as
soon as the goal amount of free memory is made.  When 'consist' tuner is
used, the reclamation was continued even after the goal amount of free
memory is made, resulting in more than goal amount of free memory, as
expected.

Patch Sequence
==============

First four patches implement the features.  Patch 1 extends core API to
allow multiple tuners and make the current tuner as the default and only
available tuner, namely 'consist'.  Patch 2 allows future tuners setting
zero effective quota.  Patch 3 introduces the second tuner, namely
'temporal'.  Patch 4 further extends DAMON sysfs API to let users use
that.

Three following patches (patches 5-7) update design, usage, and ABI
documents, respectively.

Final four patches (patches 8-11) are for adding tests.  The eighth patch
(patch 8) extends the kunit test for online parameters commit for
validating the goal_tuner.  The ninth and the tenth patches (patches 9-10)
extend the testing-purpose DAMON sysfs control helper and DAMON status
dumping tool to support the newly added feature.  The final eleventh one
(patch 11) extends the existing online commit selftest to cover the new
feature.

This patch (of 11):

DAMOS quota goal feature utilizes a single feedback loop based algorithm
for automatic tuning of the effective quota.  It is useful in dynamic
environments that operate systems with only kernels in the long term. 
But, no one fits all.  It is not very easy to control in environments
having more controlled characteristics and user-space control towers.  We
actually got multiple reports [1,2] of use cases that the algorithm is not
optimal.

Introduce a new field of 'struct damos_quotas', namely 'goal_tuner'.  It
specifies what tuning algorithm the given scheme should use, and allows
DAMON API callers to set it as they want.  Nonetheless, this commit
introduces no new tuning algorithm but only the interface.  This commit
hence makes no behavioral change.  A new algorithm will be added by the
following commit.

Link: https://lkml.kernel.org/r/20260310010529.91162-2-sj@kernel.org
Link: https://lore.kernel.org/CALa+Y17__d=ZsM1yX+MXx0ozVdsXnFqF4p0g+kATEitrWyZFfg@mail.gmail.com [1]
Link: https://lore.kernel.org/20260204022537.814-1-yunjeong.mun@sk.com [2]
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:25 -07:00
SeongJae Park
2a5f4454e0 mm/damon/core: clarify damon_set_attrs() usages 
damon_set_attrs() is called for multiple purposes from multiple places. 
Calling it in an unsafe context can make DAMON internal state polluted and
results in unexpected behaviors.  Clarify when it is safe, and where it is
being called.

Link: https://lkml.kernel.org/r/20260307195356.203753-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Acked-by: wang lian <lianux.mm@gmail.com>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:22 -07:00
SeongJae Park
5d6a520aff mm/damon/core: use mult_frac() 
Patch series "mm/damon: improve/fixup/update ratio calculation, test and
documentation".

Yet another batch of misc/minor improvements and fixups.  Use mult_frac()
instead of the worse open-coding for rate calculations (patch 1).  Add a
test for a previously found and fixed bug (patch 2).  Improve and update
comments and documentations for easier code review and up-to-date
information (patches 3-6).  Finally, fix an obvious typo (patch 7).


This patch (of 7):

There are multiple places in core code that do open-code rate
calculations.  Use mult_frac(), which is developed for doing that in a way
more safe from overflow and precision loss.

Link: https://lkml.kernel.org/r/20260307195356.203753-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20260307195356.203753-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Acked-by: wang lian <lianux.mm@gmail.com>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:22 -07:00