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b=RS4l/RZHDooKtVB05At7vYIs8ePU8T6hnTv8ahVsuEi08OIL99u9pP8En9iILpv3O 38Aj/BeJvAL3Z8xFUpsjzqO7GehatUgB8vyqhSE+PsI6Wc1etruP4Q9bjCzutdDqaA hSK4GTnriwfXlftGpNUwhii/vNnqJv2vezdgKQCQ= Date: Sun, 14 Dec 2025 15:49:44 -0800 From: Andrew Morton To: Deepanshu Kartikey Cc: axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, 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 Subject: Re: [PATCH] mm: vmscan: always allow writeback during memcg reclaim Message-Id: <20251214154944.6a6e91ffb00677a5164074e9@linux-foundation.org> In-Reply-To: <20251213083639.364539-1-kartikey406@gmail.com> References: <20251213083639.364539-1-kartikey406@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 4mpm3nyp4ppgpu1e8kcki36tgbcoiu3k X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 12554C000E X-Rspam-User: X-HE-Tag: 1765756186-488325 X-HE-Meta: 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 YdXLMzC2 2NdU2eQpqR7h59DBrjSVCKN0CR1E5j/zgbunBkQ4pnO4qf+Bc247ev4HgHifeb1hRRdjJ6EpCCLaH3Vl/6vpTy9muYgGB9j6FZD5t3QAuAFxi06fmnBuBmprYgxhW1KeFAcqE+dinb616p1WBGcHYf1rjRcuIdBlmFPG2JkzWMyYzJOttCDbNFk2Wgfsc/kWUQhKAqQZtvc3L0wifFsLeyIiESvosCZ1juHwcMuTIM7g+841JWkVTL86jHH281RReLWwSQq7u9oShk3Nx5yeGJKbjlR538SMMLLYfwpGk0HQMdQIpkVSYHC3SKjP8dmlv+ZiRyjaoMJwSL8b8PvGV1wxjkMgjOB131C4qwaB9FfxixKetjfYKhrKTFg== 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 Sat, 13 Dec 2025 14:06:39 +0530 Deepanshu Kartikey wrote: > When laptop_mode is enabled, may_writepage is set to 0 in > try_to_free_mem_cgroup_pages(). This triggers a warning in MGLRU's > lru_gen_shrink_lruvec(): > > VM_WARN_ON_ONCE(!sc->may_writepage || !sc->may_unmap); > > The warning occurs because MGLRU expects full reclaim capabilities to > function correctly. The call path is: > > mem_cgroup_resize_max() > try_to_free_mem_cgroup_pages() > do_try_to_free_pages() > shrink_node() > shrink_lruvec() > lru_gen_shrink_lruvec() <-- WARNING > > Unlike kswapd or direct reclaim where laptop_mode's disk-saving behavior > is a reasonable optimization, memcg limit enforcement is a hard > requirement - memory MUST be freed when a cgroup exceeds its limit. > The may_unmap field is already set unconditionally to 1 in this path, > acknowledging that memcg reclaim needs full capabilities. > > Set may_writepage unconditionally to 1 for memcg reclaim to ensure > MGLRU works correctly and memory limits are properly enforced. > Thanks, I'll add this to mm.git's mm-new branch for testing. I expect a few days after that I'll quietly move it into the mm-unstable branch where it will receive linux-next exposure. Further progress into mm.git's non-rebasing for-next-merge-window mm-stable branch will depend upon review outcomes.