From: Li Wang <liwang@redhat.com>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: Waiman Long <longman@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
Tejun Heo <tj@kernel.org>, Shuah Khan <shuah@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
Sean Christopherson <seanjc@google.com>,
James Houghton <jthoughton@google.com>,
Sebastian Chlad <sebastianchlad@gmail.com>,
Guopeng Zhang <zhangguopeng@kylinos.cn>,
Li Wang <liwan@redhat.com>
Subject: Re: [PATCH v2 1/7] memcg: Scale up vmstats flush threshold with int_sqrt(nr_cpus+2)
Date: Thu, 2 Apr 2026 18:19:56 +0800 [thread overview]
Message-ID: <ac5CzJ5S0kp71rrs@redhat.com> (raw)
In-Reply-To: <ac42aIDVaGim5moO@redhat.com>
> > with kernel functions:
> > var1 = 65536*nr_cpus / (45426 * ilog2(nr_cpus) + 65536)
> > var2 = DIV_ROUND_UP(65536*nr_cpus, 45426 * ilog2(nr_cpus) + 65536)
> > var3 = roundup_pow_of_two(var2)
Consider a 1024-CPU machine with a cpuset-constrained cgroup using only 2 CPUs.
Its unavoidable batching error is just 2MB, yet the global threshold imposes
256MB (harmonic-mean) or 32MB (sqrt) of additional error — 128x and 16x
overprovisioning respectively. Both overshoot, but sqrt stays bit closer to
the ideal.
--
Regards,
Li Wang
next prev parent reply other threads:[~2026-04-02 10:20 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-20 20:42 [PATCH v2 0/7] selftests: memcg: Fix test_memcontrol test failures with large page sizes Waiman Long
2026-03-20 20:42 ` [PATCH v2 1/7] memcg: Scale up vmstats flush threshold with int_sqrt(nr_cpus+2) Waiman Long
2026-03-23 12:46 ` Li Wang
2026-03-24 0:15 ` Yosry Ahmed
2026-03-25 16:47 ` Waiman Long
2026-03-25 17:23 ` Yosry Ahmed
2026-04-01 18:41 ` Michal Koutný
2026-04-02 9:27 ` Li Wang
2026-04-02 10:19 ` Li Wang [this message]
2026-03-20 20:42 ` [PATCH v2 2/7] memcg: Scale down MEMCG_CHARGE_BATCH with increase in PAGE_SIZE Waiman Long
2026-03-23 12:47 ` Li Wang
2026-03-24 0:17 ` Yosry Ahmed
2026-03-20 20:42 ` [PATCH v2 3/7] selftests: memcg: Iterate pages based on the actual page size Waiman Long
2026-03-23 2:53 ` Li Wang
2026-03-23 2:56 ` Li Wang
2026-03-25 3:33 ` Waiman Long
2026-03-20 20:42 ` [PATCH v2 4/7] selftests: memcg: Increase error tolerance in accordance with " Waiman Long
2026-03-23 8:01 ` Li Wang
2026-03-25 16:42 ` Waiman Long
2026-03-20 20:42 ` [PATCH v2 5/7] selftests: memcg: Reduce the expected swap.peak with larger " Waiman Long
2026-03-23 8:24 ` Li Wang
2026-03-25 3:47 ` Waiman Long
2026-03-20 20:42 ` [PATCH v2 6/7] selftests: memcg: Don't call reclaim_until() if already in target Waiman Long
2026-03-23 8:53 ` Li Wang
2026-03-20 20:42 ` [PATCH v2 7/7] selftests: memcg: Treat failure for zeroing sock in test_memcg_sock as XFAIL Waiman Long
2026-03-23 9:44 ` Li Wang
2026-03-21 1:16 ` [PATCH v2 0/7] selftests: memcg: Fix test_memcontrol test failures with large page sizes Andrew Morton
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