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b=fb+oI0eBop/lWoz0ykKSm5KiAODDbkMzthqi5lEDcZbXhmawKdxmvKUZlrMSLL5PS WnA4FFrXioEhVBwA/MDsJY3AvT0V/VcNxZGboSI/HOTbXyGdUVwkxas/74LSk0uii/ zVpzGzSl0rfU9bcw3B7zmujjcecVRAWXkcOOBSTTajJjH8Nd/rP6DVvByHPLOHVa0N 3R8JwhT9IA4e9ASMFqsqD1iZ4WW1ME2waj267TBw8inlQpPe/fhUuST5M5u0KGhXGy fctI61XJdFcOmj6F+pJIuEY0soaFsU4jtbhkx4uCEHngq7j1ju+2uNyZgrl37M6S92 CUmJa8kRXhh4g== Message-ID: <82da5375-bae0-4a12-af2c-de82d18769e1@kernel.org> Date: Fri, 18 Sep 2026 15:34:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] mm: memcg: don't hand out large folios above memory.high To: Shakeel Butt , Qinyun Tan 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 References: <20260915042546.279410-1-qinyuntan@linux.alibaba.com> <20260915042546.279410-2-qinyuntan@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 930AC140013 X-Stat-Signature: tboq9r73ysmh3xqjnmd3a7d49ywgix79 X-Rspam-User: X-HE-Tag: 1789738471-700721 X-HE-Meta: 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 Cdv6Oc4F mHFhiaIvWrh60DjABZL/+wt4j1+y/tudvaZWLlXpddHuTXM3wUChY/ZDzpX9JiOHZHd5GKZGdubW2FAoviqHOhxgJQezhAgYM51xgnCmEKLjRSFujss6P5GnwF1izyn732B4cNAagPv0GMqr11966RlT8hr7NwM0dBJ5rAK6KG1YzWa/AIBz8KZOFMVIPD6YCYEui8/ME292lmyHGHZEFwuLZLx6KtHnbh2nNR4j3lgy1692neHCuMFro3WLO0Fy87jqr Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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