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AJvYcCXusJtaizjPdMXW6FMvxkV32Jlf+AVdzdqrnJwxBz78UNlM+70GaCJ65V9MFQWbdaWxUgWSgmojlg==@kvack.org X-Gm-Message-State: AOJu0YzYr0n3gHJ7oGQIwj4ObNoofSx9KocSzBwSF8azH2G72FfYu8gR 43UsSQNIv1TDqIsW3JKzDHT229+K7VTigekK3lYg8nh5pCja4zszaCf4THbztfuCvI5NM5znR0e HsEpVQUBmRh2vDC2VE5sC0698pAcaG74TJMLjug5I X-Gm-Gg: ATEYQzymc8J98k+1HFuIK+LQmIubcSaHq8R5S+HYRHbv/SKU6aa8i0hNnIoxvPEAomq D5wckYxkuqnR5LLs1U9e8K/p9YE2VdxoNKjm+9zJ3DSrVYIlksbOPJf0pvWQBm6k2g/GuNq/ngC Vg2/WW+hFNCM4F+jMLnrSiNtmf0WKSJCrA2rt3euCHnK0mDOmAgf7eUj161xr3lJFZqHfVC98ET ieaGvtchA2GOGU+IOOs5PP4R5N2h8rbxZUtJyTOZmXNMmdZ0ReEhMpjyiwAd2G5QbyXk5+OQ3VM lc5PtA== X-Received: by 2002:aa7:d1cc:0:b0:65a:1240:b8c4 with SMTP id 4fb4d7f45d1cf-6694d002a64mr43286a12.3.1774283176120; Mon, 23 Mar 2026 09:26:16 -0700 (PDT) MIME-Version: 1.0 References: <20260322070843.941997-1-surenb@google.com> <65cb38ee-2815-4b11-929d-3fc1528cc620@lucifer.local> In-Reply-To: <65cb38ee-2815-4b11-929d-3fc1528cc620@lucifer.local> From: Suren Baghdasaryan Date: Mon, 23 Mar 2026 09:26:02 -0700 X-Gm-Features: AQROBzAnXd6fOd5-0DtwGKGuyxDjiwJX4YSM6ZsiwuTxV14NkOPK2l2DDkj64jw Message-ID: Subject: Re: [PATCH 1/1] mm/vmscan: prevent MGLRU reclaim from pinning address space To: "Lorenzo Stoakes (Oracle)" Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, zhengqi.arch@bytedance.com, yuzhao@google.com, shakeel.butt@linux.dev, willy@infradead.org, Liam.Howlett@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 9j71j8bkeex76h7s4gtox3e6amp1zqqa X-Rspamd-Queue-Id: 6AEAD40007 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1774283178-710835 X-HE-Meta: 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 4O0aqre2 yi4dYeiX89td5AQbNV0sITfqphyoon7I4zLJAUoTNUBP32UUZh4e0jktjaz6fJ7uM+AW0TT9iM1thJfQ1S5L4o8ToY/mLN+x+VLC0IMLLbxpnvSQmxWWTPnq9jJjBsoN63Lw6ve7TJj+TkWPjO2pD77G2VaKhIHJ/s5p8Y3gix7CkZSNL0NZX3hSAuEVdyzKsKl0E9IriEwjlA6eauGZYJn7b47fEYNHr0zwulf9FNiEsLzQljKhcwhJUXaCzE3IvV1RwF5UumeafEl0RLS0CAfBht2+fj9ET9Opv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 23, 2026 at 6:43=E2=80=AFAM Lorenzo Stoakes (Oracle) wrote: > > On Sun, Mar 22, 2026 at 12:08:43AM -0700, Suren Baghdasaryan wrote: > > When shrinking lruvec, MGLRU pins address space before walking it. > > This is excessive since all it needs for walking the page range is > > a stable mm_struct to be able to take and release mmap_read_lock and > > a stable mm->mm_mt tree to walk. This address space pinning results > > in delays when releasing the memory of a dying process. This also > > prevents mm reapers (both in-kernel oom-reaper and userspace > > process_mrelease()) from doing their job during MGLRU scan because > > they check task_will_free_mem() which will yield negative result due > > to the elevated mm->mm_users. > > > > Replace unnecessary address space pinning with mm_struct pinning by > > replacing mmget/mmput with mmgrab/mmdrop calls. mm_mt is contained > > within mm_struct itself, therefore it won't be freed as long as > > mm_struct is stable and it won't change during the walk because > > mmap_read_lock is being held. > > > > Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks") > > Signed-off-by: Suren Baghdasaryan > > Oh and sorry, missed this - do we need a 'Fixed' for something that's jus= t a > perf improvement? > > This doesn't seem buggy? Well, if we are pinning something we should not is that a bug? I didn't CC stable, so I don't expect it to be backported (though if it's accepted, we will backport it in Android as it causes real problems with reclaim), however if someone is looking for MGLRU fixes I would like this patch to be discoverable. If you feel strongly about it, I'll remove the tag. Thanks for the review! > > Thanks, Lorenzo