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b=srPRDA9yRhiPLbMsiJDPRUPs9V2ZzT1YQObGxngCh3yI6TMcMJqDDMptnr0UFNfO4 H8JYgliPQxwe4TjOVsrO2hlq9Yeot+FMTiaTSll7ozxIMV1uNBqN/1B5LyFQxwn+cz Jor79O5R5NBW4rA4q1hADdJyVQghSwmybBUhU3LaTQ6LyZw/7U41CYnKCv/c7OqNSZ EczkCypYIxIZwkeRcxtH9LK5FYYpT7jvswnwmsaOGqP2vbr0jvOlN8VVnrgQ6hnBkV Fc+Tz1kowYl6cvREIp38CzUfwLEb22AZ3FKb9GpXX4r5KTV63VUFrVwk8xNyks+3mj 4bEqunXHbXUZg== Date: Mon, 23 Mar 2026 13:43:52 +0000 From: "Lorenzo Stoakes (Oracle)" To: Suren Baghdasaryan 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 Subject: Re: [PATCH 1/1] mm/vmscan: prevent MGLRU reclaim from pinning address space Message-ID: <65cb38ee-2815-4b11-929d-3fc1528cc620@lucifer.local> References: <20260322070843.941997-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260322070843.941997-1-surenb@google.com> X-Rspam-User: X-Rspamd-Queue-Id: 5261918000D X-Rspamd-Server: rspam08 X-Stat-Signature: rsdxa1jto5afp9c6zf13z6iwjtyyoe6k X-HE-Tag: 1774273437-753244 X-HE-Meta: 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 7D5aCwI+ Axkjvz1LlDDgTFWoa7uaErD82/htCf+XPEZQ8rU38zWoYWEXdpCOD7MkhEdYdL70aN+zV7q/keq9IswiVfBvp0CMBFsOAn6/hmzYnKCHtweBhEeZqRHrrCNgVORnBZetanPAb4kT1SuyoQQt+GwW/FPp5CetJtSzsRonbrC3uc0KgKhpKeVkXdlFLd7g42NDKPIMCKb0xc6Xo9RpNXuEaxKYk2cjZNiY1LvV9DvPq4c+Fraw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 just a perf improvement? This doesn't seem buggy? Thanks, Lorenzo