Hi Johannes,

On Fri, Mar 12, 2021 at 11:23 AM Johannes Weiner [off-list ref] wrote:

[...]

Longer term we most likely need it there anyway. The issue you are
describing in the cover letter - allocations pinning memcgs for a long
time - it exists at a larger scale and is causing recurring problems
in the real world: page cache doesn't get reclaimed for a long time,
or is used by the second, third, fourth, ... instance of the same job
that was restarted into a new cgroup every time. Unreclaimable dying
cgroups pile up, waste memory, and make page reclaim very inefficient.

For the scenario described above, do we really want to reparent the
page cache pages? Shouldn't we recharge the pages to the second,
third, fourth and so on, memcgs? My concern is that we will see a big
chunk of page cache pages charged to root and will only get reclaimed
on global pressure.