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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-930b54773fbsm912994185a.39.2026.07.20.10.26.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Jul 2026 10:26:14 -0700 (PDT) Date: Mon, 20 Jul 2026 13:26:09 -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 v2 01/15] mm/vma: introduce VMA virtual page offset field and add helpers Message-ID: References: <20260720-b4-scalable-cow-virt-pgoff-v2-0-2d549757a76f@kernel.org> <20260720-b4-scalable-cow-virt-pgoff-v2-1-2d549757a76f@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jul 20, 2026 at 05:56:52PM +0100, Lorenzo Stoakes (ARM) wrote: > On Mon, Jul 20, 2026 at 11:49:00AM -0400, Gregory Price wrote: > > On Mon, Jul 20, 2026 at 03:38:27PM +0100, Lorenzo Stoakes (ARM) wrote: > > > > > > The virtual 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. > > > > > > > The latter half of this description is a bit confusing. > > > > Why would the value differ from (vma->vm_start >> PAGE_SHIFT)? > > (because it's file backed? > > Because the VMA gets remapped. > > If it's remapped when it's unfaulted, then virtual page offset gets updated, if > it's faulted then not. > ahhhhh the wording is just wonky then when faulted or remapped, x is... when unfaulted or unremapped, x is... instead of x is ... if unfaulted or were not remapped, otherwise... Sort of a complex combination of 3 negatives there. ~Gregory