linux-kernel - Re: [PATCH v6 1/2] mm/vmscan: Skip memcg with !usage in shrink_node

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Message-ID: <uaxa3qttqmaqxsphwukrxdbfrx6px7t4iytjdksuroqiu6w7in@75o4bigysttw>
Date: Mon, 14 Apr 2025 15:55:39 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Waiman Long <llong@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Tejun Heo <tj@...nel.org>, Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v6 1/2] mm/vmscan: Skip memcg with !usage in
 shrink_node_memcgs()

On Mon, Apr 14, 2025 at 09:15:57AM -0400, Waiman Long <llong@...hat.com> wrote:
> I did see some low event in the no usage case because of the ">=" comparison
> used in mem_cgroup_below_min().

Do you refer to A/B/E or A/B/F from the test?
It's OK to see some events if there was non-zero usage initially.

Nevertheless, which situation this patch changes that is not handled by
mem_cgroup_below_min() already?

> Yes, low event count for E is 0 in the !memory_recursiveprot case, but C/D
> still have low events and setting no_low_events_index to -1 will fail the
> test and it is not the same as not checking low event counts at all.

I added yet another ignore_low_events_index variable (in my original
proposal) not to fail the test. But feel free to come up with another
implementation, I wanted to point out the "not specified" expectation
for E with memory_recursiveprot.

Michal

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