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

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Message-ID: <0fd86682-0679-48ee-8622-d9d7a977d69c@redhat.com>
Date: Mon, 27 Oct 2025 10:34:43 +0100
From: David Hildenbrand <david@...hat.com>
To: "Kirill A. Shutemov" <kirill@...temov.name>,
 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 24.10.25 21:32, Kirill A. Shutemov wrote:
> 
> 
> 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().

Ah, I missed that we can also have folio sizes besides PMD_SIZE here.

So it's all about testing whether the complete folio would be mapped by 
a single page table.

(a helper would be nice, but cannot immediately come up with a good name)

-- 
Cheers

David / dhildenb