From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
To: Gregory Price <gourry@gourry.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
"Liam R. Howlett" <liam@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Jann Horn <jannh@google.com>,
Pedro Falcato <pfalcato@suse.de>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Jan Kara <jack@suse.cz>, Miaohe Lin <linmiaohe@huawei.com>,
Naoya Horiguchi <nao.horiguchi@gmail.com>,
Rik van Riel <riel@surriel.com>, Harry Yoo <harry@kernel.org>,
Lance Yang <lance.yang@linux.dev>, Kees Cook <kees@kernel.org>,
Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Nico Pache <npache@redhat.com>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>,
Usama Arif <usama.arif@linux.dev>,
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Rakie Kim <rakie.kim@sk.com>, Byungchul Park <byungchul@sk.com>,
Ying Huang <ying.huang@linux.alibaba.com>,
Alistair Popple <apopple@nvidia.com>,
Peter Xu <peterx@redhat.com>, Xu Xin <xu.xin16@zte.com.cn>,
Chengming Zhou <chengming.zhou@linux.dev>,
Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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
Date: Mon, 20 Jul 2026 17:56:52 +0100 [thread overview]
Message-ID: <al5Surm6fPIl4LNA@lucifer> (raw)
In-Reply-To: <al5CPpc7XpRX7Vbt@gourry-fedora-PF4VCD3F>
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.
That's because when faulted folios may reference the original offset :)
Scalable CoW will likely change this but that's a forthcoming series of many
series :P
>
> It sounds like this value can change in response to an event, which
> makes me thing a reader could see two values across two calls?
Remapping :) and no a reader cannot (locking etc. :P)
>
> Apologies if i'm fundamentally misunderstanding something.
No that's a sign that probably I'm not being clear enough! Can try to clarify on
next respin.
>
> ~Gregory
Cheers, Lorenzo
next prev parent reply other threads:[~2026-07-20 16:57 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-20 14:38 [PATCH v2 00/15] mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 01/15] mm/vma: introduce VMA virtual page offset field and add helpers Lorenzo Stoakes (ARM)
2026-07-20 15:49 ` Gregory Price
2026-07-20 16:56 ` Lorenzo Stoakes (ARM) [this message]
2026-07-20 17:26 ` Gregory Price
2026-07-20 14:38 ` [PATCH v2 02/15] mm: introduce linear_virt_page_index() Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 03/15] mm: abstract vma_address() and introduce vma_anon_address() Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 04/15] mm: update print_bad_page_map() to show virtual page index Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 05/15] mm: introduce and use vma_filebacked_address() Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 06/15] mm: propagate VMA virtual page offset on map, remap, split + merge Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 07/15] mm/rmap: track whether the page VMA mapped walk is anonymous Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 08/15] mm: introduce and use linear_folio_page_index() Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 09/15] mm/rmap: use virt pgoff for MAP_PRIVATE file-backed anon folios Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 10/15] tools/testing/vma: expand VMA merge tests to assert virt pgoff Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 11/15] tools/testing/selftests/mm: test virtual page offset merge behaviour Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 12/15] mm/vma: only permit MAP_PRIVATE /dev/zero to be mapped anonymous Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 13/15] mm/vma: make MAP_PRIVATE-mapped /dev/zero mappings truly anonymous Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 14/15] tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon Lorenzo Stoakes (ARM)
2026-07-20 14:38 ` [PATCH v2 15/15] tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests Lorenzo Stoakes (ARM)
2026-07-20 19:48 ` [PATCH v2 00/15] mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff Andrew Morton
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