Re: [PATCH v2 1/2] memcg: switch lruvec stats to rstat

Hi, Shakeel,

Shakeel Butt [off-list ref] writes:

The commit 2d146aa3aa84 ("mm: memcontrol: switch to rstat") but skipped
the conversion of the lruvec stats as such stats are read in the
performance critical code paths and flushing stats may have impacted the
performances of the applications. This patch converts the lruvec stats
to rstat and later patch adds the periodic flushing of the stats and
thus remove the need to synchronously flushing the stats in the
performance critical code paths.

The rstat conversion comes with the price i.e. memory cost. Effectively
this patch reverts the savings done by the commit f3344adf38bd ("mm:
memcontrol: optimize per-lruvec stats counter memory usage"). However
this cost is justified due to negative impact of the inaccurate lruvec
stats on many heuristics. One such case is reported in [1].

The memory reclaim code is filled with plethora of heuristics and many
of those heuristics reads the lruvec stats. So, inaccurate stats can
make such heuristics ineffective. [1] reports the impact of inaccurate
lruvec stats on the "cache trim mode" heuristic. Inaccurate lruvec stats
can impact the deactivation and aging anon heuristics as well.

[1] https://lore.kernel.org/linux-mm/20210311004449.1170308-1-ying.huang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org/

Sorry for late reply.  I have just verified that this patchset can
resolve the problem as in the above link for me.  Thanks!

Best Regards,
Huang, Ying

Signed-off-by: Shakeel Butt <redacted>
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Changes since v1:
- no changes