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Sat, 28 Feb 2026 20:16:32 -0800 (PST) MIME-Version: 1.0 References: <20260225223712.3685-1-21cnbao@gmail.com> <2558f7d82b9a482387960f45409e1b76@honor.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Sun, 1 Mar 2026 12:16:21 +0800 X-Gm-Features: AaiRm52HFpwyHb-X-YItA0yeS6EGekp30FDO_EnHs5XeL0STRhlevgBNWywuDvU Message-ID: Subject: Re: [PATCH RFC] mm/mglru: lazily activate folios while folios are really mapped To: wangzicheng Cc: "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Suren Baghdasaryan , Lei Liu , "Matthew Wilcox (Oracle)" , Axel Rasmussen , Yuanchu Xie , Wei Xu , Kairui Song , Tangquan Zheng , wangtao Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: 383C71A0002 X-Rspamd-Server: rspam08 X-Stat-Signature: pbrzktbzawy8figthofpasqrthi9r7id X-HE-Tag: 1772338594-446024 X-HE-Meta: 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 X2xE0Mkw 50MWVYEoolbDCQODaoKorfaxVvTy3SBzKTAf2c/jwlMcvG75xoIwhM2lD5GItTQiVouK1qT3/rXRrY1SiOeNsrsA7KYNwfz1Evt0M Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Feb 28, 2026 at 6:28=E2=80=AFPM wangzicheng = wrote: > > Hi Barry, > > > > I find your concern a bit surprising. If I understand correctly, > > you=E2=80=99re observing that file folios are currently being over-recl= aimed. > > In that case, placing hot pages at the tail might make them harder > > to reclaim after PTE scanning (since they may still be young), but > > this seems to violate the fundamental principle of LRU. Moreover, > > when scanning encounters young file folios, reclaim will simply > > continue scanning more folios to find reclaimable ones, so scanning > > hot folios only wastes CPU time. > > Since read-ahead cold folios are placed at the head, relatively hotter > > folios may be reclaimed instead, causing refaults and further triggerin= g > > reclaim, which can worsen the situation. > > > Thank you for the detailed explanation. > > > > > > We'll test this when available and report back. We hope to have a > > > chance to discuss this topic at LSF/MM/BPF. > > > > > > > Sure, thanks! > > > > Barry > > For evaluation I=E2=80=99m using a workload that repeatedly cold-starts a= nd > drives same user actions in 20+ apps on Android. > I=E2=80=99m comparing baseline(v6.6) vs. the patched kernel and watching > `/proc/vmstat -> workingset_refault_file`, expecting it to go down. > > I ran 3 runs per kernel, but `workingset_refault_file` is quite noisy, > the Coefficient of Variation is around 40%, so the result doesn=E2=80=99t= look > statistically solid. > > Do you have any suggestions on how to measure the benefit more > robustly? For example: > - different or longer-running workloads, > - better normalization for refaults (per time, per faults, etc.), > - or other vmstat metrics that you found more stable in practice? I've cc'ed Tangquan, and he may be able to share how he was testing. Basically, you may want to disable Wi-Fi, as it can introduce a lot of variability between runs. Aside from refault metrics, you should also see reduced I/O load and fewer swap-out/in events if you run the same sequence of apps consistently. > > I=E2=80=99m also considering increasing the number of runs and using a t-= test, > or comparing the CDF between baseline and patched kernels. > If you have a preferred methodology, I=E2=80=99d like to align with that. > Thanks Barry