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

From: Chris Down
Date: Tue Jul 28 2020 - 15:45:04 EST

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
(, 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@xxxxxxxxxxx>

Acked-by: Chris Down <chris@xxxxxxxxxxxxxx>