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Tue, 10 Feb 2026 17:00:56 -0800 (PST) MIME-Version: 1.0 References: <20260210043456.2137482-1-haowenchao22@gmail.com> In-Reply-To: From: Wenchao Hao Date: Wed, 11 Feb 2026 09:00:45 +0800 X-Gm-Features: AZwV_QjpXVDS1vTxoDUxsGlc-RNprzDKM4R84OmSvVdHky4zyhqDegSLPUXTTXc Message-ID: Subject: Re: [RFC PATCH] mm: only set fault addrsss' access bit in do_anonymous_page To: Kiryl Shutsemau Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 2126180009 X-Stat-Signature: rsrghmyh7oknjnsgt8io1a1761my4zqp X-Rspam-User: X-HE-Tag: 1770771656-915011 X-HE-Meta: U2FsdGVkX1/Y4nmTbd5zLpchXtnmYkvSk9o7NzHkSKNOZ0D122qXerqVdyFfLeYsyo341eDRcKoaBZFsrO5um7a60EEKl/6KFk1Ty20fGTAp+GRQP7U82bW2rh8E455WnsOqM/VPRbCcyVO9cET0NYMhKnJ5+xvZXBLaH9tC0uWX+8mjpdkNso3fydZMacU+TVQJ+EeujFASrwC7sHkP7RdfBAehjyF4whiADXA8YiV8Fn+SBGOOASvwCIRlUsRNP1k1Z8iT1sD8lIJTAJQs05T18TKeR5tF5tOiAtuRk1J5w3YtXtCzhmSi8wQlskpo1PnFD2lU0wwOEscixsdHdTljLtPCVGZvidHpof0dZv0FshKwTi62zibwVVhFXALu0NHj9j8LmXS5I9b0m0uimuUsR7Qm3uD13PFruzh+fNHKk7JV8i8xRq/1ky+F66yUZ3YPtBGKjoGHU6qzvWmEYA0dZFPMoDQfggcJPXB1afe2EqEANTEWhJXrqHsp9eHFG7qEXhwwgDRkvbzY+4GrCEB9rVyC2w373tCp17KpJVXTjTsf4lfi7WfpZMX6Rxch2rP2MgfdqDyWY1VL70zF1K9I0m+Rsy7DQM7QNai5nouFBb+MHnD5z/nDXQ1n0UECZm15KJZdRnxdr5b+3CoICb47hBrV5LpH08YJOnsYG45QjfsthwSdQIRlDUGPVEVfSAlbb8HVF9YSVadFJndIEuMhMfQdvLHxdt34uu6zl1yaz5unRCbQxQwMaYkcLsCEqWdCa3tMEN8AJPURRFTzGcDIsXtbSf2i8zPcCMM6y+8HB+c0uM2jlnhigi1gRBFlJ+gBwUahTvj+et+Uc7Ki2DXWnmE0IYs121SrYWRTI0bKY69gEFfBVDcnG/xRdM3BFTcAzHcpb3wilGwbxER5onxy+ZAZESpqHNh7P7Js8W+XPjZvIQmaw1p36HXocsOzs20GYwaNUXc8SMS9iuG d+7glKa/ MKNBIXUZVBXhe7hoLCLo2t37K7/SpZ0OL1tQalqVIupnSecpBHGmOOWWgrYsnQw0WCHofrzLWNLY2QF256grUMBu3xOfaCiig84sunp/85m36L4jfN0fvKbZXOdPSffgK+qe7dY5CKPLBbQtLqNqwio3kdA2Q4l0s3rpXqPxktd24anF7HsTWxDv9tsfQys0P2olKuAAftud1/3YLxF81oaInUWiwjBAqhAbIf/8ZuoIjfzU5MeqzFQkLlETvZH8Xoq2oU9a+DihysPnByEoRl6m563bHkGc9Y9C2zuS3wnpjx144JDjgwqKnKpBq8zeMEULS9jMv/eaxjhessPaSPO7/4iBxeS/lmo3V3tVgpsvdVRNXtrdCu6tWVEY0Qx/Vz9+pRSgi/cvZjnw0aZs+20VfDDnx2Ira2yu01e6fxuvU7rm+CcENJmsydr+IWqW1RNjj 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 Tue, Feb 10, 2026 at 7:56=E2=80=AFPM Kiryl Shutsemau wrote: > > On Tue, Feb 10, 2026 at 12:34:56PM +0800, Wenchao Hao wrote: > > When do_anonymous_page() creates mappings for huge pages, it currently = sets > > the access bit for all mapped PTEs (Page Table Entries) by default. > > > > This causes an issue where the Referenced field in /proc/pid/smaps cann= ot > > distinguish whether a page was actually accessed. > > > > So here introduces a new interface, set_anon_ptes(), which only sets th= e > > access bit for the PTE corresponding to the faulting address. This allo= ws > > accurate tracking of page access status in /proc/pid/smaps before memor= y > > reclaim scan the folios. > > > > During memory reclaim: folio_referenced() checks and clears the access = bits > > of PTEs, rmap verifies all PTEs under a folio. If any PTE mapped subpag= e of > > folio has access bit set, the folio is retained during reclaim. So only > > set the access bit for the faulting PTE in do_anonymous_page() is safe,= as > > it does not interfere with reclaim decisions. > > We had similar discussion about faultaround and briefly made it produce > old ptes, but it caused performance regression as old ptes require > additional pagewalk to set accessed bit on touch. It got reverted, > but arch can opt-in for setting up old ptes for non-fault address. > > See commits: > > 5c0a85fad949 ("mm: make faultaround produce old ptes") > 315d09bf30c2 ("Revert "mm: make faultaround produce old ptes"") > 46bdb4277f98 ("mm: Allow architectures to request 'old' entries when pref= aulting") > It does look similar=E2=80=94our modifications both revolve around whether = pre-mapped PTEs should be marked as "new." Was there any analysis into why your changes led to performance regressions= ? This could help guide whether my modifications are meaningful, and perhaps = I could reference your approach to implement similar changes for different architectures. > -- > Kiryl Shutsemau / Kirill A. Shutemov