From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Shakeel Butt <shakeel.butt@linux.dev>,
Qinyun Tan <qinyuntan@linux.alibaba.com>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@suse.com,
roman.gushchin@linux.dev, muchun.song@linux.dev, ljs@kernel.org,
ziy@nvidia.com, baolin.wang@linux.alibaba.com,
xlpang@linux.alibaba.com, liam@infradead.org,
nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com,
baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev,
vbabka@kernel.org, rppt@kernel.org, surenb@google.com,
chris@chrisdown.name, kasong@tencent.com, linux-mm@kvack.org,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/1] mm: memcg: don't hand out large folios above memory.high
Date: Fri, 18 Sep 2026 15:34:22 +0200 [thread overview]
Message-ID: <82da5375-bae0-4a12-af2c-de82d18769e1@kernel.org> (raw)
In-Reply-To: <aqx5kcqRrbkuay4i@linux.dev>
On 9/18/26 03:26, Shakeel Butt wrote:
> On Tue, Sep 15, 2026 at 12:25:46PM +0800, Qinyun Tan wrote:
>> memory.high is enforced on return to userspace, and synchronously in
>
> Over time I feel like this sync throttle for memory.high was a bad decision but
> that is an orthogonal discussion.
>
>> try_charge_memcg() for large overcharges, but only when the charge gfp
>> allows blocking. A populate loop - mlock(), MADV_POPULATE_*, any
>> GUP-driven population - never returns to userspace, and large folios are
>> charged with the THP allocation gfp, which does not allow blocking under
>> the default defrag=madvise without MADV_HUGEPAGE, nor under defrag=defer.
>> So neither runs: usage grows from memory.high straight up to memory.max
>> with no reclaim and no penalty sleep.
>>
>> mlock(200M) in a cgroup with memory.high=30M and memory.max=140M. Of the
>> 110M between high and max, the burst consumed:
>>
>> 4K pages 3M in 5s, then still throttled
>> THP, defrag=always 6M in 5s, then still throttled
>> THP, defrag=madvise 110M in 13ms, then OOM killed at 16ms
>> THP, defrag=madvise, patched 3M in 5s, then still throttled
>
> I don't really like polluting non-memcg MM code with memcg internal details.
That's the same thought I had when skimming the code.
--
Cheers,
David
next prev parent reply other threads:[~2026-09-18 13:34 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-15 4:25 [PATCH v2 0/1] mm: memcg: don't hand out large folios above memory.high Qinyun Tan
2026-09-15 4:25 ` [PATCH v2 1/1] " Qinyun Tan
2026-09-18 1:26 ` Shakeel Butt
2026-09-18 3:36 ` Qinyun Tan
2026-09-18 13:34 ` David Hildenbrand (Arm) [this message]
2026-09-18 13:52 ` [PATCH v2 0/1] " Lorenzo Stoakes (ARM)
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