github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-08-01 12:11:59 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph
Linux kernel source tree
1,398,025 Commits 1 Branch 940 Tags 24 GiB
C 96.9%
Assembly 0.9%
Rust 0.6%
Shell 0.6%
Python 0.5%
Other 0.3%
9fb749cd15
Go to file
Kairui Song 9fb749cd15 mm, swap: do not perform synchronous discard during allocation 
Patch series "mm, swap: misc cleanup and bugfix", v2.

A few cleanups and a bugfix that are either suitable after the swap table
phase I or found during code review.

Patch 1 is a bugfix and needs to be included in the stable branch, the
rest have no behavioral change.


This patch (of 5):

Since commit 1b7e90020e ("mm, swap: use percpu cluster as allocation
fast path"), swap allocation is protected by a local lock, which means we
can't do any sleeping calls during allocation.

However, the discard routine is not taken well care of.  When the swap
allocator failed to find any usable cluster, it would look at the pending
discard cluster and try to issue some blocking discards.  It may not
necessarily sleep, but the cond_resched at the bio layer indicates this is
wrong when combined with a local lock.  And the bio GFP flag used for
discard bio is also wrong (not atomic).

It's arguable whether this synchronous discard is helpful at all.  In most
cases, the async discard is good enough.  And the swap allocator is doing
very differently at organizing the clusters since the recent change, so it
is very rare to see discard clusters piling up.

So far, no issues have been observed or reported with typical SSD setups
under months of high pressure.  This issue was found during my code
review.  But by hacking the kernel a bit: adding a mdelay(500) in the
async discard path, this issue will be observable with WARNING triggered
by the wrong GFP and cond_resched in the bio layer for debug builds.

So now let's apply a hotfix for this issue: remove the synchronous discard
in the swap allocation path.  And when order 0 is failing with all cluster
list drained on all swap devices, try to do a discard following the swap
device priority list.  If any discards released some cluster, try the
allocation again.  This way, we can still avoid OOM due to swap failure if
the hardware is very slow and memory pressure is extremely high.

This may cause more fragmentation issues if the discarding hardware is
really slow.  Ideally, we want to discard pending clusters before
continuing to iterate the fragment cluster lists.  This can be implemented
in a cleaner way if we clean up the device list iteration part first.

Link: https://lkml.kernel.org/r/20251024-swap-clean-after-swap-table-p1-v2-0-a709469052e7@tencent.com
Link: https://lkml.kernel.org/r/20251024-swap-clean-after-swap-table-p1-v2-1-c5b0e1092927@tencent.com
Fixes: 1b7e90020e ("mm, swap: use percpu cluster as allocation fast path")
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2025-11-16 17:28:19 -08:00
arch iommu/sva: invalidate stale IOTLB entries for kernel address space 2025-11-16 17:28:18 -08:00
block block-6.18-20251031 2025-10-31 12:57:19 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto This push contains the following changes: 2025-10-10 08:56:16 -07:00
Documentation doc: update porting, vfs documentation for mmap_prepare actions 2025-11-16 17:28:13 -08:00
drivers iommu/sva: invalidate stale IOTLB entries for kernel address space 2025-11-16 17:28:18 -08:00
fs mm: update resctl to use mmap_prepare 2025-11-16 17:28:14 -08:00
include iommu/sva: invalidate stale IOTLB entries for kernel address space 2025-11-16 17:28:18 -08:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring mm: consistently use current->mm in mm_get_unmapped_area() 2025-11-16 17:27:57 -08:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel relay: update relay to use mmap_prepare 2025-11-16 17:28:11 -08:00
lib lib/test_vmalloc: remove xfail condition check 2025-11-16 17:27:53 -08:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm mm, swap: do not perform synchronous discard during allocation 2025-11-16 17:28:19 -08:00
net Including fixes from bluetooth and wireless. 2025-11-06 08:52:30 -08:00
rust rust: kbuild: workaround rustdoc doctests modifier bug 2025-11-04 00:00:06 +01:00
samples Char/Misc/IIO/Binder changes for 6.18-rc1 2025-10-04 16:26:32 -07:00
scripts scripts/decode_stacktrace.sh: fix build ID and PC source parsing 2025-11-09 21:19:45 -08:00
security integrity-v6.18 2025-10-05 10:48:33 -07:00
sound ASoC: Fixes for v6.18 2025-10-30 13:08:08 +01:00
tools mm: add ability to take further action in vm_area_desc 2025-11-16 17:28:12 -08:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM x86 fixes for 6.18: 2025-10-18 10:25:43 +02:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap MAINTAINERS: update David Hildenbrand's email address 2025-11-15 10:52:01 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS MAINTAINERS: update David Hildenbrand's email address 2025-11-15 10:52:01 -08:00
Makefile Linux 6.18-rc5 2025-11-09 15:10:19 -08:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.