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mm/damon/stat: add a parameter for reading kdamond pid

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Patch series "mm/damon/stat: add kdamond_pid parameter".

DAMON_STAT doesn't provide the pid of its kdamond, unlike DAMON_RECLAIM
and DAMON_LRU_SORT.  This makes user-space management of DAMON_STAT
unnecessarily complicated.  Provide the information via a new parameter,
namely kdamond_pid, and document it.


This patch (of 2):

Knowing the pid of the kdamonds can help user-space management including
monitoring of DAMON's system resource consumption.  To make it easier,
DAMON_SYSFS, DAMON_RECLAIM and DAMON_LRU_SORT provide the pid information.
DAMON_STAT is not providing it, though.  Expose the pid of DAMON_STAT
kdamond via a new read-only module parameter, namely kdamond_pid.  This
also makes DAMON modules usage more standardized, because DAMON_RECLAIM
and DAMON_LRU_SORT also provide the information via their read-only
parameters of the same name.

Link: https://lore.kernel.org/20260502020505.80822-1-sj@kernel.org
Link: https://lore.kernel.org/20260502020505.80822-2-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>
This commit is contained in:
SeongJae Park 2026-05-01 19:05:03 -07:00 committed by Andrew Morton
parent 1794454a3b
commit 3a0bc9568c
1 changed files with 39 additions and 0 deletions
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39
mm/damon/stat.c
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@ -266,6 +266,45 @@ static int damon_stat_enabled_load(char *buffer, const struct kernel_param *kp)
return sprintf(buffer, "%c\n", damon_stat_enabled() ? 'Y' : 'N');
}
static int damon_stat_kdamond_pid_store(
const char *val, const struct kernel_param *kp)
{
/*
* kdamond_pid is read-only, but kernel command line could write it.
* Do nothing here.
*/
return 0;
}
static int damon_stat_kdamond_pid_load(
char *buffer, const struct kernel_param *kp)
{
int pid;
if (!damon_stat_context) {
pid = -1;
} else {
pid = damon_kdamond_pid(damon_stat_context);
if (pid < 1)
pid = -1;
}
return sprintf(buffer, "%d\n", pid);
}
static const struct kernel_param_ops kdamond_pid_param_ops = {
.set = damon_stat_kdamond_pid_store,
.get = damon_stat_kdamond_pid_load,
};
/*
* PID of the DAMON thread
*
* If DAMON_STAT is enabled, this becomes the PID of the worker thread.
* Else, -1.
*/
module_param_cb(kdamond_pid, &kdamond_pid_param_ops, NULL, 0400);
MODULE_PARM_DESC(kdamond_pid, "pid of the kdamond");
static int __init damon_stat_init(void)
{
int err = 0;