memcg: enable memcg oom-kill for __GFP_NOFAIL

In the era of async memcg oom-killer, the commit a0d8b00a ("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 29ef680a ("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 1f14c1ac
("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.

Link: https://lkml.kernel.org/r/20210223204337.2785120-1-shakeelb@google.com


Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>