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From: Shakeel Butt To: Kiryl Shutsemau Cc: Andrew Morton , David Hildenbrand , Hugh Dickins , Matthew Wilcox , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Rik van Riel , Harry Yoo , Johannes Weiner , 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-Migadu-Flow: FLOW_OUT X-Stat-Signature: 94y3rdtj8jziuqruzw1hkfuyen385t7y X-Rspam-User: X-Rspamd-Queue-Id: C4432120003 X-Rspamd-Server: rspam10 X-HE-Tag: 1758317319-338276 X-HE-Meta: U2FsdGVkX1+64SlzT2XKIJolJHPu4o5HCKWTNRfiUgfrPd4AndrUFcXsmnJMExQeLag4zeat8nakuAf4c8ynu2FxdBoEJYQ3NN6y3IwQwp/rXpIIHfeHcE7zCOP3/C4aQipTBmBdYQAArS4eZKyesvZLCT2906RTeaKApdV2E9pUYDZxMBbY6dyJzPKng/RvVbeM7eXKwAJbgqR+9HFzRHyJLihEmnUkRmkmMJxEkr7fcuLPYUqvte10Yd/Io8+wAo7esjw3MDeDwHx6NWyRvTrq1N4FK2BeflAfab0p+KGqYTgi0zih1A5VZh5Rt2jgTHbUS1ji1CsmD81pNs4SQMlH8qNyfVvv2heenUC8RfwE/EYeL7vM02yhFv1fHxN33dY2jVl28MzwHGnGl8lIgk8/QRahTeABK8zmAAhYUrGSJH8T0Wju1m6mUOgItoiyofGMuWMGE1hXE2+AALwYuywdfQDLEmSFI2WpI+aSmAe326xJeA5iI0JWunn1JB2rJwgzvhv+REQoRIN2/HmkWoEIdBYKBTrjb8u46BiwOHfTYnBxgI6id4Vu7kQu8lSocn+KJf6gU7EceKbgm4CAvn3By+NZ+DbE97LyYM4MfQIK/oA457eqlcX5imvGqbkh2UwBRcBx85KLr7usoc+iikKuGtjr4XR7uMQzOLx4npVFKJ9bGjCAx4qj2Cuv/U0IssPPsJFUWIRk2gu4fl8co5Ba8zFz90l+Wx3g4TP+JJezkAOIosvD2kjSAH8D5l8SFAawdjGNi4iDowcFBD/4gseXHlmIpASqzXpr0Imb1AvHJXggQsgfbvA3mcAAg8//MGH68qpVff3sR9flg0lSGXGsdBTvYW851jWOCcfM25g8j1wRlV28Y/xm55+zdj34UBz8NViLRezgLGStW7cfFTsfGxwJv9XXvNV+X0k7N2Hl5MWc9QQzzCrEouY7n2MCAN2fwKnnB3cep3nJj4G tJf/Y7y4 5qvkl1xtOzhN3R/aRdkcCQumgDKn1TCMuklTL8rYJxacHma3ZYqbNDzyRJzcrCz9Vf8ajm3FJcYgwT0ey7VwR56fqfgcgP0nJM3qQZ8AhzrkJK5Ggyj1iIJTpTyLPOYbk3yT5+B9Hf32l/EcJ6bJABdOAGyrl1ajNvDBYP/Q2B0tjSPMXfGaSnIN8G7tVPx3vOM5Z8cTltY01evSqr9WO5d7tfU7vTmVCMMoxRwffTsz9A3DHr06ReeGbhIs4Ztmgfwli6xUgu65q0XV/UpUcofENUw== 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: > From: Kiryl Shutsemau > > 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. > > Signed-off-by: Kiryl Shutsemau Reviewed-by: Shakeel Butt