From 72793f5cc9e41f9ee33353d4594036817529b766 Mon Sep 17 00:00:00 2001 From: Vasily Averin Date: Sat, 11 Sep 2021 10:40:08 +0300 Subject: [PATCH] ipc: remove memcg accounting for sops objects in do_semtimedop() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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@virtuozzo.com/ Fixes: 18319498fdd4 ("memcg: enable accounting of ipc resources") Signed-off-by: Vasily Averin Acked-by: Michal Hocko Reviewed-by: Michal Koutný Acked-by: Shakeel Butt Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- ipc/sem.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/ipc/sem.c b/ipc/sem.c index 8010cd9d1d7a..d84f42196e52 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -1962,8 +1962,7 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops, 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; }