linux-kernel - Re: [PATCHv3 1/2] mm/memory: Do not populate page table entries beyond i

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Message-ID: <ctkrffqndi7tmw2d7vj5k7asotqe5z7ic4ux7wc3pqu6kyernk@sz34te5pkbmd>
Date: Mon, 3 Nov 2025 15:18:45 +0000
From: Kiryl Shutsemau <kirill@...temov.name>
To: Matthew Wilcox <willy@...radead.org>
Cc: Hugh Dickins <hughd@...gle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Rik van Riel <riel@...riel.com>, 
	Harry Yoo <harry.yoo@...cle.com>, Johannes Weiner <hannes@...xchg.org>, 
	Shakeel Butt <shakeel.butt@...ux.dev>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	"Darrick J. Wong" <djwong@...nel.org>, Dave Chinner <david@...morbit.com>, linux-mm@...ck.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/2] mm/memory: Do not populate page table entries
 beyond i_size

On Mon, Nov 03, 2025 at 02:35:57PM +0000, Matthew Wilcox wrote:
> On Mon, Nov 03, 2025 at 10:59:00AM +0000, Kiryl Shutsemau wrote:
> > On Sat, Nov 01, 2025 at 05:00:47AM +0000, Matthew Wilcox wrote:
> > > On Wed, Oct 29, 2025 at 02:45:52AM -0700, Hugh Dickins wrote:
> > > > But you're giving yourself too hard a time of backporting with your
> > > > 5.10 Fixee 01c70267053d for 1/2: the only filesystem which set the
> > > > flag then was tmpfs, which you're now excepting.  The flag got
> > > > renamed later (in 5.16) and then in 5.17 at last there was another
> > > > filesystem to set it.  So, this 1/2 would be
> > > > 
> > > > Fixes: 6795801366da ("xfs: Support large folios")
> > > 
> > > I haven't been able to keep up with this patchset -- sorry.
> > > 
> > > But this problem didn't exist until bs>PS support was added because we
> > > would never add a folio to the page cache which extended beyond i_size
> > > before.  We'd shrink the folio order allocated in do_page_cache_ra()
> > > (actually, we still do, but page_cache_ra_unbounded() rounds it up
> > > again).  So it doesn't fix that commit at all, but something far more
> > > recent.
> > 
> > What about truncate path? We could allocate within i_size at first, then
> > truncate, if truncation failed to split the folio the mapping stays
> > beyond i_size.
> 
> Is it worth backporting all this way to solve this niche case?

Dave says it is correctness issue, so.. yes?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov