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

[Chris Down <chris-6Bi1550iOqEnzZ6mRAm98g@public.gmane.org>]

Johannes Weiner writes:
>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. 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.

Seems totally reasonable, and the patch looks fine too.

>Signed-off-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>

Acked-by: Chris Down <chris-6Bi1550iOqEnzZ6mRAm98g@public.gmane.org>