The patch titled
Subject: memcg, oom: remove explicit wakeup in mem_cgroup_oom_synchronize()
has been added to the -mm mm-unstable branch. Its filename is
memcg-oom-remove-explicit-wakeup-in-mem_cgroup_oom_synchronize.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-oom-remove-explicit-wakeup-in-mem_cgroup_oom_synchronize.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Haifeng Xu <haifeng.xu@xxxxxxxxxx>
Subject: memcg, oom: remove explicit wakeup in mem_cgroup_oom_synchronize()
Date: Wed, 19 Apr 2023 03:07:39 +0000
Before commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
charge path"), all memcg oom killers were delayed to page fault path. And
the explicit wakeup is used in this case:
thread A:
...
if (locked) { // complete oom-kill, hold the lock
mem_cgroup_oom_unlock(memcg);
...
}
...
thread B:
...
if (locked && !memcg->oom_kill_disable) {
...
} else {
schedule(); // can't acquire the lock
...
}
...
The reason is that thread A kicks off the OOM-killer, which leads to
wakeups from the uncharges of the exiting task. But thread B is not
guaranteed to see them if it enters the OOM path after the OOM kills but
before thread A releases the lock.
Now only oom_kill_disable case is handled from the #PF path. In that case
it is userspace to trigger the wake up not the #PF path itself. All
potential paths to free some charges are responsible to call
memcg_oom_recover() , so the explicit wakeup is not needed in the
mem_cgroup_oom_synchronize() path which doesn't release any memory itself.
Link: https://lkml.kernel.org/r/20230419030739.115845-2-haifeng.xu@xxxxxxxxxx
Signed-off-by: Haifeng Xu <haifeng.xu@xxxxxxxxxx>
Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
--- a/mm/memcontrol.c~memcg-oom-remove-explicit-wakeup-in-mem_cgroup_oom_synchronize
+++ a/mm/memcontrol.c
@@ -2028,15 +2028,8 @@ bool mem_cgroup_oom_synchronize(bool han
mem_cgroup_unmark_under_oom(memcg);
finish_wait(&memcg_oom_waitq, &owait.wait);
- if (locked) {
+ if (locked)
mem_cgroup_oom_unlock(memcg);
- /*
- * There is no guarantee that an OOM-lock contender
- * sees the wakeups triggered by the OOM kill
- * uncharges. Wake any sleepers explicitly.
- */
- memcg_oom_recover(memcg);
- }
cleanup:
current->memcg_in_oom = NULL;
css_put(&memcg->css);
_
Patches currently in -mm which might be from haifeng.xu@xxxxxxxxxx are
cpuset-clean-up-cpuset_node_allowed.patch
memcg-oom-remove-unnecessary-check-in-mem_cgroup_oom_synchronize.patch
memcg-oom-remove-explicit-wakeup-in-mem_cgroup_oom_synchronize.patch
