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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Rik van Riel , Harry Yoo , Johannes Weiner , Shakeel Butt , Baolin Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kiryl Shutsemau Subject: Re: [PATCHv2 4/5] mm/fault: Try to map the entire file folio in finish_fault() Message-ID: References: <20250919124036.455709-1-kirill@shutemov.name> <20250919124036.455709-5-kirill@shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250919124036.455709-5-kirill@shutemov.name> X-Rspamd-Queue-Id: A5978140007 X-Rspamd-Server: rspam05 X-Stat-Signature: ubz4et6ar14xqxmpr1dy531ed333xs4w X-Rspam-User: X-HE-Tag: 1758353875-799633 X-HE-Meta: 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 28gw+vBE l9AZR5FRBxJ2rUcnWblu9Y8SXdTQBR9f5gfkLhd6f4rWVxZmFTsRjCBoEB8SdNBrCrojK61YyZRHEi4NyC0FK/sRyNgFCfDMXYbBz+CVYohjPz+Czg+Wt0fN8GVS4xJzMHLskPZSOhlTIzgxoxhz/tGecQ61gWUWfVDerhIeAsztTgGfhBSehpzSl5Px0dd0YBD8OmATEU0DOcc1zygqeFdUVkhj3OlAdjTnz X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.