Re: [PATCH 1/4] memcg: enable accounting for large allocations in mem_cgroup_css_alloc

Shakeel Butt
2022-05-20T01:07:07Z

On Fri, May 13, 2022 at 06:51:41PM +0300, Vasily Averin wrote:
> cgroup mkdir can be misused inside memcg limited container. It can allocate
> a lot of host memory without memcg accounting, cause global memory shortage
> and force OOM to kill random host process.
>
> Below [1] is result of mkdir /sys/fs/cgroup/test tracing on VM with 4 cpus
>
> number bytes $1*$2 sum note call_site
> of alloc
> allocs
> ------------------------------------------------------------
> 1 14448 14448 14448 = percpu_alloc_percpu:
> 1 8192 8192 22640 (mem_cgroup_css_alloc+0x54)
> 49 128 6272 28912 (__kernfs_new_node+0x4e)
> 49 96 4704 33616 (simple_xattr_alloc+0x2c)
> 49 88 4312 37928 (__kernfs_iattrs+0x56)
> 1 4096 4096 42024 (cgroup_mkdir+0xc7)
> 1 3840 3840 45864 = percpu_alloc_percpu:
> 4 512 2048 47912 (alloc_fair_sched_group+0x166)
> 4 512 2048 49960 (alloc_fair_sched_group+0x139)
> 1 2048 2048 52008 (mem_cgroup_css_alloc+0x109)
> [smaller objects skipped]
> ---
> Total 61728
>
> '=' -- accounted allocations
>
> This patch enabled accounting for one of the main memory hogs in this
> experiment: allocation which are called inside mem_cgroup_css_alloc()
>
> Signed-off-by: Vasily Averin <vvs-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
> Link: [1] https://lore.kernel.org/all/1aa4cd22-fcb6-0e8d-a1c6-23661d618864-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org/
>

Acked-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>