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AJvYcCX5y6cMzL/DovzNXVSezTWzmFMDAIR8XXcuJBGXVYC3IEiGflkuySwOW8jdGoPlItsdklNL0XdfnFvN+daOahZckEM= X-Gm-Message-State: AOJu0Yy9eC7uskw0FKp3fPnXxVOOpR2KNP3Y2R9FCjE6CouW2jUYYv4M u9M/1mM+chz8BU/aHaBnORkrD3VbGuF5kd72SeN13eQSsOxmLCStoZXVTav68TFUTVpFv17sytg mMQMecQdoPUAn9zoYaS90ZLSm1RqP5lgrWcvm X-Google-Smtp-Source: AGHT+IH8DQAMUWESkE3uI4SAFspU5Lmkmnbb+Jk0Ftbm42szLeCxXAaqh0w+gS9vCMjP4HyEG3RJiRM+c5urdMop850= X-Received: by 2002:a05:6122:1d48:b0:4f6:a7f7:164d with SMTP id 71dfb90a1353d-4fad1da735dmr398339e0c.8.1723569416350; Tue, 13 Aug 2024 10:16:56 -0700 (PDT) MIME-Version: 1.0 References: <20240813163759.742675-1-yuanchu@google.com> In-Reply-To: <20240813163759.742675-1-yuanchu@google.com> From: Yu Zhao Date: Tue, 13 Aug 2024 11:16:19 -0600 Message-ID: Subject: Re: [PATCH] mm: multi-gen LRU: ignore non-leaf pmd_young for force_scan=true To: Yuanchu Xie Cc: Andrew Morton , Lance Yang , Huang Ying , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 8DADC18000F X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: br4zex8oumwem8qf56nrph3o7ukoj3b7 X-HE-Tag: 1723569417-476374 X-HE-Meta: U2FsdGVkX1+zN/tCpmWMmTIWrDQW0Ok/1E3iqdEzHEPi1Ue3ubBrskKhefc/I/K//iRo4ulUORmysYK4APCp4WojkpQr1jQ0yQNioJ8E9BuSPg6EMjQ76Z0ocau7LKKLO/LDwH/E1i6o8sydPOiUgy6a6E0kCunYC2+oyb/x3Y8t3BkZor1w62KGkEz6y6TfqHfXXyfwYnuzbIQWcAlY0qGcJG+4Bu6WEhuPcfQIEdAVbtZ43IqLgPaym9zxNdhqRmrzYYv6FathBBtRdCOuNnJ4jTXwdqlmHFBwhz7oeclJ+ieEdSfJr7YW4ompise0mPAwYXQfQQMNUnSd84/byEGP3p7bIiJ68F4tPn+10zkKI1tiOS5bemsRYSV2ZAw8IuySU3Ieixs+6vgUclNRwfBA+vWxfPm70zkaecuVEvaL1uHSALmxuZahUoZiy2SFixbCfUvxHnGaw0JVII13tJUq1rzTBg0Uk6zlGjNQN0AqtSwb8xkVbJWTb1QCjWfFYi0d1wAscwyByf1qPL8Leh9ngs/0MnGPr5HbjbyiY8tVxR/gT4ZREcBCscfZovv1UHzZemqwP2MNlKZy4uSDTJSSUiTO8Gljze1jKWXdZ28xj7srRCzGQAEBMgmnqViynV5xnW5m2HDpQVTXMmOQxbJNRQhKBZmPDpPiCASfPBPdhke4iPBo57n53w1PNcC/r9XtcFAJa3YZg2mA6EBuUywu+B7gmmk38K7KED0GaRb/3rwTPAYIXjHRpxNE0YWajjkUphc1JK/PRKHWaWH/X62DCQ67FNaAYtcl3FAM2VCCef8Ih9zHQEvR/2jDdjxZ2Z00d9Vovjfbl/4MGTbHMI/BrxL6VgN3txmcLuapd84fPaHq4tATif93hb4lz86fDtoOqfL6Rc2xc4tt/3v3rk2n7C3JTVA2OeeJJ1HV84MmuWxMH+kBTGWykEOCJyBZycLvnBip3LVAcZkj6gT OAUoyQWa 63qBoMINsHmQ+c73dG5TtyRYaGzVupU5iLrs44pr1Aulg+OclxCeJsVksg0zIMsaR/qrm2cfZJdQsjuztVr5snoPwXhh4yQYYKV3A86LPd6913RKAXfLaKv1rRrwGdNM7vDwarszw/U8QH9OcTfDTR5DkLdmSBYER0MThGJ/N4a8gMxdhC+H7YVHYdRlBbeL8yZpc3+/06WZfdwhQhz67r9gvsCoX7siVLSvDdOpry6J2nLM= 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, Aug 13, 2024 at 10:38=E2=80=AFAM Yuanchu Xie w= rote: > > When non-leaf pmd accessed bits are available, MGLRU page table walks > can clear the non-leaf pmd accessed bit and ignore the accessed bit on > the pte if it's on a different node, skipping a generation update as > well. If another scan occurs on the same node as said skipped pte. > the non-leaf pmd accessed bit might remain cleared and the pte accessed > bits won't be checked. While this is sufficient for reclaim-driven > aging, where the goal is to select a reasonably cold page, the access > can be missed when aging proactively for workingset estimation of a > node/memcg. > > In more detail, get_pfn_folio returns NULL if the folio's nid !=3D node > under scanning, so the page table walk skips processing of said pte. Now > the pmd_young flag on this pmd is cleared, and if none of the pte's are > accessed before another scan occurs on the folio's node, the pmd_young > check fails and the pte accessed bit is skipped. > > Since force_scan disables various other optimizations, we check > force_scan to ignore the non-leaf pmd accessed bit. > > Signed-off-by: Yuanchu Xie Acked-by: Yu Zhao