From: Matthew Wilcox <willy@infradead.org>
To: Kiryl Shutsemau <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@redhat.com>,
Hugh Dickins <hughd@google.com>,
Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
"Liam R. Howlett" <Liam.Howlett@oracle.com>,
Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>,
Harry Yoo <harry.yoo@oracle.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeel.butt@linux.dev>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Kiryl Shutsemau <kas@kernel.org>
Subject: Re: [PATCHv2 4/5] mm/fault: Try to map the entire file folio in finish_fault()
Date: Sat, 20 Sep 2025 08:37:37 +0100 [thread overview]
Message-ID: <aM5ZwWiFDOuSl6C5@casper.infradead.org> (raw)
In-Reply-To: <20250919124036.455709-5-kirill@shutemov.name>
On Fri, Sep 19, 2025 at 01:40:35PM +0100, Kiryl Shutsemau wrote:
> The finish_fault() function uses per-page fault for file folios. This
> only occurs for file folios smaller than PMD_SIZE.
>
> The comment suggests that this approach prevents RSS inflation.
> However, it only prevents RSS accounting. The folio is still mapped to
> the process, and the fact that it is mapped by a single PTE does not
> affect memory pressure. Additionally, the kernel's ability to map
> large folios as PMD if they are large enough does not support this
> argument.
>
> When possible, map large folios in one shot. This reduces the number of
> minor page faults and allows for TLB coalescing.
>
> Mapping large folios at once will allow the rmap code to mlock it on
> add, as it will recognize that it is fully mapped and mlocking is safe.
Does this patch have any measurable effect? Almost all folios are
mapped through do_fault_around(). I'm not objecting to the patch,
but the commit message maybe makes this sound more important than it is.
next prev parent reply other threads:[~2025-09-20 7:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-19 12:40 [PATCHv2 0/5] mm: Improve mlock tracking for large folios Kiryl Shutsemau
2025-09-19 12:40 ` [PATCHv2 1/5] mm/page_vma_mapped: Track if the page is mapped across page table boundary Kiryl Shutsemau
2025-09-19 20:25 ` Shakeel Butt
2025-09-22 16:13 ` Kiryl Shutsemau
2025-09-19 12:40 ` [PATCHv2 2/5] mm/rmap: Fix a mlock race condition in folio_referenced_one() Kiryl Shutsemau
2025-09-19 21:18 ` Shakeel Butt
2025-09-19 12:40 ` [PATCHv2 3/5] mm/rmap: mlock large folios in try_to_unmap_one() Kiryl Shutsemau
2025-09-19 21:27 ` Shakeel Butt
2025-09-22 9:51 ` Kiryl Shutsemau
2025-09-22 20:16 ` Shakeel Butt
2025-09-19 12:40 ` [PATCHv2 4/5] mm/fault: Try to map the entire file folio in finish_fault() Kiryl Shutsemau
2025-09-19 21:28 ` Shakeel Butt
2025-09-20 7:37 ` Matthew Wilcox [this message]
2025-09-22 16:16 ` Kiryl Shutsemau
2025-09-22 3:19 ` Baolin Wang
2025-09-19 12:40 ` [PATCHv2 5/5] mm/rmap: Improve mlock tracking for large folios Kiryl Shutsemau
2025-09-22 3:20 ` Baolin Wang
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