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Thu, 18 Dec 2025 21:14:30 -0800 (PST) MIME-Version: 1.0 References: <20251213083639.364539-1-kartikey406@gmail.com> <20251215041200.GB905277@cmpxchg.org> In-Reply-To: From: Kairui Song Date: Fri, 19 Dec 2025 13:13:53 +0800 X-Gm-Features: AQt7F2rKOI2q1UqKgR3tTirk88okwlFfOXhEExrJt2rJNuSNabtVRH3HRJpenLY Message-ID: Subject: Re: [PATCH] mm: vmscan: always allow writeback during memcg reclaim To: Yuanchu Xie Cc: Deepanshu Kartikey , Johannes Weiner , akpm@linux-foundation.org, axelrasmussen@google.com, weixugc@google.com, david@kernel.org, mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com, yuzhao@google.com, heftig@archlinux.org, oleksandr@natalenko.name, bgeffon@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+90fcab4d88cffed6d0d8@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 9BB2E20011 X-Stat-Signature: z4zy9p5f5ce54giw96q74sgpxqbe8kex X-HE-Tag: 1766121272-194477 X-HE-Meta: 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 dUV9p1Za 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 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, Dec 16, 2025 at 3:52=E2=80=AFAM Yuanchu Xie wr= ote: > > On Sun, Dec 14, 2025 at 10:52=E2=80=AFPM Deepanshu Kartikey > wrote: > > > > On Mon, Dec 15, 2025 at 9:42=E2=80=AFAM Johannes Weiner wrote: > > > > > > Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks") > > > > > > That seems unrelated? > > > > Sorry for the wrong fixes. Correct Fixes: ee814fe23daf ("mm: vmscan: > > clean up struct scan_control") > > > > I'll wait for input from someone with MGLRU context on the broader disc= ussion. > > > This warning came from commit e9d4e1ee7880 ("mm: multi-gen LRU: > clarify scan_control flags") [1]. > > The original rationale: > > 4. sc->may_writepage and sc->may_unmap, which indicates opportunistic > > reclaim, are rejected, since unmapped clean folios are already > > prioritized. Scanning for more of them is likely futile and can > > cause high reclaim latency when there is a large number of memcgs. > > As far as I can tell this was a sanity check to ensure > `lru_gen_shrink_lruvec` avoids extra work for minimal gain. Perhaps > this shouldn't be a warning? Always setting may_writepage in this case > would free more folios. I'm not against removing the warning either. > > @Wei Xu @Axel Rasmussen Any opinions? > > [1] https://lore.kernel.org/all/20221222041905.2431096-8-yuzhao@google.co= m/T/#u > Hi All, We are also hitting this warning in our test environment. Simply removing that WARN seems OK for us, shrink_folio_list will bounce these folios back and everything behaves just fine. Meanwhile, is it a good idea to add back the !sc->may_unmap check in isolate_folio or improve isolate_folios accordingly? That might help reduce the overhead in the worst scenarios.