Re: [PATCH] memcg: Optimize exit to user space

[Roman Gushchin]

Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes:

> memcg uses TIF_NOTIFY_RESUME to handle reclaiming on exit to user
> space. TIF_NOTIFY_RESUME is a multiplexing TIF bit, which is utilized by
> other entities as well.
>
> This results in a unconditional mem_cgroup_handle_over_high() call for
> every invocation of resume_user_mode_work(), which is a pointless
> exercise as most of the time there is no reclaim work to do.
>
> Especially since RSEQ is used by glibc, TIF_NOTIFY_RESUME is raised
> quite frequently and the empty calls show up in exit path profiling.
>
> Optimize this by doing a quick check of the reclaim condition before
> invoking it.
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> Cc: Muchun Song <muchun.song@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>

Thanks!