linux-kernel - Re: [PATCHv2 1/2] mm/memory: Do not populate page table entries beyond i

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Message-Id: <ca03ba53-388d-4ac4-abf3-062dcdf6ff00@app.fastmail.com>
Date: Fri, 24 Oct 2025 20:32:36 +0100
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: "David Hildenbrand" <david@...hat.com>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Hugh Dickins" <hughd@...gle.com>, "Matthew Wilcox" <willy@...radead.org>,
 "Alexander Viro" <viro@...iv.linux.org.uk>,
 "Christian Brauner" <brauner@...nel.org>
Cc: "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 <linux-mm@...ck.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>,
 linux-kernel@...r.kernel.org, "Kiryl Shutsemau" <kas@...nel.org>
Subject: Re: [PATCHv2 1/2] mm/memory: Do not populate page table entries beyond i_size

On Fri, Oct 24, 2025, at 16:42, David Hildenbrand wrote:
> On 23.10.25 11:32, Kiryl Shutsemau wrote:
>>   	addr0 = addr - start * PAGE_SIZE;
>>   	if (folio_within_vma(folio, vmf->vma) &&
>> -	    (addr0 & PMD_MASK) == ((addr0 + folio_size(folio) - 1) & PMD_MASK)) {
>> +	    (addr0 & PMD_MASK) == ((addr0 + folio_size(folio) - 1) & PMD_MASK) &&
>
> Isn't this just testing whether addr0 is aligned to folio_size(folio)? 
> (given that we don't support folios > PMD_SIZE), like
>
> 	IS_ALIGNED(addr0, folio_size(folio))

Actually, no. VMA can be not aligned to folio_size().

-- 
Kiryl Shutsemau / Kirill A. Shutemov