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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-908323eb01esm6949626d6.30.2026.07.29.20.32.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jul 2026 20:32:07 -0700 (PDT) Date: Wed, 29 Jul 2026 23:32:04 -0400 From: Gregory Price To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Miaohe Lin , Naoya Horiguchi , Rik van Riel , Harry Yoo , Lance Yang , Kees Cook , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Ying Huang , Alistair Popple , Peter Xu , Xu Xin , Chengming Zhou , Arnd Bergmann , Greg Kroah-Hartman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v3 01/15] mm/vma: introduce VMA anon page offset field and add helpers Message-ID: References: <20260729-b4-scalable-cow-virt-pgoff-v3-0-e8ecfefea812@kernel.org> <20260729-b4-scalable-cow-virt-pgoff-v3-1-e8ecfefea812@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260729-b4-scalable-cow-virt-pgoff-v3-1-e8ecfefea812@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: D290B180003 X-Stat-Signature: 9yejoxe1kxuuthyfeo4kbuontz9m74y9 X-HE-Tag: 1785382330-417765 X-HE-Meta: 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 wflKlN3x 81WBOfa6zvBKQCBcutlsfINvqRpAODuLeEEH4ERUa9K3CTpchTstA8VfY/k/F5FLNzYVFTHQN/qQ6swuEn/OHVQAtWa0lJYhngQO0/VvQQkoVvTxzI6QqH4qivATZXkYppHk9qbX4rbdGvxBMVI3HX+46yikktatriANQFf+823Z65OKm+9jqRiG6GmZ0qHZvCa9qkWZoWVZhwxk6gNMntC/skD7QrlxK2zs/IwD9pzBZTHopUcNG14G/1kWhCprG79MHJHvZbvnSx/Ls4LuNdlQrpBu1S0FcRdj703OXmXQPt7qubShJbqNpo8Zvbv1Y3h/jTBcETZQcPm2o1YgR7Gsx0ItFwYHyUb6nVj8zdb1+tm/cnRUJuP1uDrcC498hf/sB08AygPno/J2wWfwrhte06pjBKj9G4h5Mk6KAzMV8BPIV2p70nj1WAWPyxMJ3amTvx0R0BLlkRFmvWDJYZ78KzZkvepzoCadQjCB/j2JpGJ4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 29, 2026 at 05:48:36PM +0100, Lorenzo Stoakes (ARM) wrote: > This patch establishes fields within the vm_area_struct type to store the > anonymous page offset of VMAs. > > The anonymous page offset of a VMA is equal to vma->vm_start >> PAGE_SHIFT > if they are unfaulted or were not remapped, otherwise it is equal to this > value at the point of first fault. > > Currently, anonymous folios belonging to CoW'd MAP_PRIVATE-mapped > file-backed VMAs are tracked by their file offset. By adding anonymous > offset as a property of VMAs, we can now track them by their anonymous page > offset instead. > > By tracking this, we provide the means by which to eliminate this > inconsistency, and more importantly lay the foundations for future work for > the scalable CoW anonymous rmap rework. > > This patch simply adds the fields and some simple helpers. Subsequent > patches will update mm code to make use of these fields correctly. > > The fields chosen are packed in the VMA such that, for 64-bit kernel > builds, no additional space is taken up. > > The first field is present on cacheline 0 containing key VMA fields, and > the second on cacheline 3, which contains file-backed reverse mapping > fields. > > Given the relative time spent accessing reverse mapping fields as well as > updating them, there shouldn't be any performance impact here from false > sharing. > > Update the VMA userland tests to account for this change. > > No callsites are updated yet, so no functional change intended. > > Signed-off-by: Lorenzo Stoakes (ARM) Much clearer :], appreciate the rewording. Reviewed-by: Gregory Price (Meta)