Re: [PATCH] mm: memcontrol: don't count limit-setting reclaim as memory pressure

[Shakeel Butt]

On Tue, Jul 28, 2020 at 6:53 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> When an outside process lowers one of the memory limits of a cgroup
> (or uses the force_empty knob in cgroup1), direct reclaim is performed
> in the context of the write(), in order to directly enforce the new
> limit and have it being met by the time the write() returns.
>
> Currently, this reclaim activity is accounted as memory pressure in
> the cgroup that the writer(!) belongs to. This is unexpected.

Indeed this is unexpected.

> It
> specifically causes problems for senpai
> (https://github.com/facebookincubator/senpai), which is an agent that
> routinely adjusts the memory limits and performs associated reclaim
> work in tens or even hundreds of cgroups running on the host. The
> cgroup that senpai is running in itself will report elevated levels of
> memory pressure, even though it itself is under no memory shortage or
> any sort of distress.
>
> Move the psi annotation from the central cgroup reclaim function to
> callsites in the allocation context, and thereby no longer count any
> limit-setting reclaim as memory pressure. If the newly set limit
> causes the workload inside the cgroup into direct reclaim, that of
> course will continue to count as memory pressure.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>