This is a note to let you know that I've just added the patch titled
ipc: remove memcg accounting for sops objects in do_semtimedop()
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ipc-remove-memcg-accounting-for-sops-objects-in-do_semtimedop.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6a4746ba06191e23d30230738e94334b26590a8a Mon Sep 17 00:00:00 2001
From: Vasily Averin <vvs@xxxxxxxxxxxxx>
Date: Sat, 11 Sep 2021 10:40:08 +0300
Subject: ipc: remove memcg accounting for sops objects in do_semtimedop()
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From: Vasily Averin <vvs@xxxxxxxxxxxxx>
commit 6a4746ba06191e23d30230738e94334b26590a8a upstream.
Linus proposes to revert an accounting for sops objects in
do_semtimedop() because it's really just a temporary buffer
for a single semtimedop() system call.
This object can consume up to 2 pages, syscall is sleeping
one, size and duration can be controlled by user, and this
allocation can be repeated by many thread at the same time.
However Shakeel Butt pointed that there are much more popular
objects with the same life time and similar memory
consumption, the accounting of which was decided to be
rejected for performance reasons.
Considering at least 2 pages for task_struct and 2 pages for
the kernel stack, a back of the envelope calculation gives a
footprint amplification of <1.5 so this temporal buffer can be
safely ignored.
The factor would IMO be interesting if it was >> 2 (from the
PoV of excessive (ab)use, fine-grained accounting seems to be
currently unfeasible due to performance impact).
Link: https://lore.kernel.org/lkml/90e254df-0dfe-f080-011e-b7c53ee7fd20@xxxxxxxxxxxxx/
Fixes: 18319498fdd4 ("memcg: enable accounting of ipc resources")
Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1984,8 +1984,7 @@ static long do_semtimedop(int semid, str
if (nsops > ns->sc_semopm)
return -E2BIG;
if (nsops > SEMOPM_FAST) {
- sops = kvmalloc_array(nsops, sizeof(*sops),
- GFP_KERNEL_ACCOUNT);
+ sops = kvmalloc_array(nsops, sizeof(*sops), GFP_KERNEL);
if (sops == NULL)
return -ENOMEM;
}
Patches currently in stable-queue which might be from vvs@xxxxxxxxxxxxx are
queue-5.4/memcg-enable-accounting-of-ipc-resources.patch
queue-5.4/ipc-remove-memcg-accounting-for-sops-objects-in-do_semtimedop.patch
