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Howlett" , Vlastimil Babka , Suren Baghdasaryan , kernel-team@meta.com Subject: Re: [PATCH v2 0/3] mm: __access_remote_vm with per-VMA lock Message-ID: References: <20260625015053.2445008-1-riel@surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260625015053.2445008-1-riel@surriel.com> X-Rspam-User: X-Stat-Signature: wwg11dejbyuin419888945wtms9o7db3 X-Rspamd-Queue-Id: 195B820002 X-Rspamd-Server: rspam06 X-HE-Tag: 1782550796-845545 X-HE-Meta: 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 1ya3GU/8 tZzR4VKDM9cAEGwH6NwCJBkvJEAlLb/VES9N/y0SgRgD15akPIZFQCOVlRVDlRqIAsoOlQGj7huyApUaTUALsl3l/6LR4gs9KCc/SLTGi9zV9vYsG71l7ghcdUvUX7mPxzafndejCP6FQF6P+jOMBipSpy3fCi4IG9FXT7XT54m2J5X3+KbYCkzFgVgUmoSXLPBnbJwpbabshvMRR1Qh/U2c1wGZy7OJT02uUTCHh92HJreEs9AgbBo3MT7/efpBFROY9xZcpXJYMXs8dd20CrHrKyS1JmmREDpnaujsePTSRfe8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jun 24, 2026 at 09:50:50PM -0400, Rik van Riel wrote: > Sometimes processes can get stuck with the mmap_lock held for > a long time. This slows down, and can even prevent system monitoring > tools from assessing and logging the situation, because they themselves > end up getting stuck on the mmap_lock. > > However, with the introduction of per-VMA locks, we can improve the > reliability of system monitoring, and generally speed up __access_remote_vm > under mmap_loc contention, by adding a fast path that does not require > the process-wide mmap_lock. > > This fast path is only compiled in and used when it is safe to do so, > meaning a kernel with per-VMA locks, RCU pgae table freeing, the VMA > is not hugetlbfs, iomap, pfnmap, etc... > > v2: > - simplify the code, which should be ok because these copies are < PAGE_SIZE > - clean up the code > - fix locking wrt tlb_remove_table_sync_one() > - hopefully address all the other comments Please always send a diffstat in your cover letter by the way. I noticed you didn't do this elsewhere also, so please adjust your tooling to do this :) (git format-patch --cover-letter does this by default). Thanks, Lorenzo