[Devel] [PATCH RHEL COMMIT] ms/ipc: remove memcg accounting for sops objects in do_semtimedop()

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.vz9.1.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after ark-5.14
------>
commit d857b183f29858b83ca26379759745bd383341f6
Author: Vasily Averin <vvs at virtuozzo.com>
Date:   Tue Sep 28 14:16:26 2021 +0300

    ms/ipc: remove memcg accounting for sops objects in do_semtimedop()
    
    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 <vvs at virtuozzo.com>
    
    Acked-by: Michal Hocko <mhocko at suse.com>
    Reviewed-by: Michal Koutný <mkoutny at suse.com>
    Acked-by: Shakeel Butt <shakeelb at google.com>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    (cherry picked from commit 6a4746ba06191e23d30230738e94334b26590a8a)
    https://jira.sw.ru/browse/PSBM-133990
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 ipc/sem.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 1a8b9f0ac047..4c4fdf010793 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2005,8 +2005,7 @@ 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;
 	}