Re: [PATCH] memcg: enable memcg oom-kill for __GFP_NOFAIL

Johannes Weiner
2021-02-24T20:39:15Z

On Tue, Feb 23, 2021 at 12:43:37PM -0800, Shakeel Butt wrote:
> In the era of async memcg oom-killer, the commit a0d8b00a3381 ("mm:
> memcg: do not declare OOM from __GFP_NOFAIL allocations") added the code
> to skip memcg oom-killer for __GFP_NOFAIL allocations. The reason was
> that the __GFP_NOFAIL callers will not enter aync oom synchronization
> path and will keep the task marked as in memcg oom. At that time the
> tasks marked in memcg oom can bypass the memcg limits and the oom
> synchronization would have happened later in the later userspace
> triggered page fault. Thus letting the task marked as under memcg oom
> bypass the memcg limit for arbitrary time.
>
> With the synchronous memcg oom-killer (commit 29ef680ae7c21 ("memcg,
> oom: move out_of_memory back to the charge path")) and not letting the
> task marked under memcg oom to bypass the memcg limits (commit
> 1f14c1ac19aa4 ("mm: memcg: do not allow task about to OOM kill to bypass
> the limit")), we can again allow __GFP_NOFAIL allocations to trigger
> memcg oom-kill. This will make memcg oom behavior closer to page
> allocator oom behavior.
>
> Signed-off-by: Shakeel Butt <shakeelb@google.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>