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Mercier" Cc: roman.gushchin@linux.dev, muchun.song@linux.dev, Andrew Morton , Kairui Song , Qi Zheng , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm/vmscan: remove redundant !mem_cgroup_online() checks Message-ID: References: <20261028010611.3929937-1-tjmercier@google.com> <20261028010611.3929937-2-tjmercier@google.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261028010611.3929937-2-tjmercier@google.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B23AB2000A X-Stat-Signature: yk8hyqutd31m5u91tuihohxekhossbr3 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793222811-404800 X-HE-Meta: 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 e60OluJ9 v3lK6/SdEXEpiMl4It9LygM6FZOeK90Q8aWvbQ37O/MU6XYVrLiUYm4fsziO2m1X5+FQgjO3oAugGS+jsuaWQb4KfAd/+RtK5oeqQNtWQtmqSP356qepCB9h1GJTb3OBM9opW0h1hpuiAlPOAg1aZ1GMQE1n1tDvg/e13zXuQS/4tYU4u4gsebcxsThP6HmL62gU5Y6y9y8Y/8eb3Pz0UWzIl11DmuLYPPUYAVFq6NHcsj/DXna8IRYfI1a1yV9ylBsLtlTWiWXrYLTZyXvyne1+5g1fJzzKgFavj2xZxmlODFnY1AaKm6qq5Gt/67Q+PFbmJc1Z68fnRJM+dg2tanQzIZ8U7DR3ec6oFXe/iEEq0V99801q/4IrcWMzTcyaPNvfa Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Oct 27, 2026 at 06:06:05PM -0700, T.J. Mercier wrote: > Since commit f1cf8d2f36dc ("mm: memcontrol: eliminate the problem of > dying memory cgroup for LRU folios") and commit 0e0ac326c511 ("memcg: > move LRU size accounting on reparenting instead of copying it"), > mem_cgroup_css_offline() reparents all LRU folios to the parent memcg > and zeroes the child's lrugen->nr_pages and lru_zone_size before the > memcg is offlined. Nothing can repopulate the offlined memcg's lruvec > afterwards. A folio that is off the LRU during reparenting looks up its > lruvec through its objcg, which now points to the parent so it is put > back on the parent's LRU. > > As a result, lruvec_lru_size() and lruvec_evictable_size() are always 0 > when !mem_cgroup_online(memcg) is true, making the offlined memcg special > cases in get_scan_count(), lruvec_is_sizable(), and shrink_one() dead > code. Remove them. > > With the get_nr_to_scan() special case removed, an offlined memcg that > still has stale effective protection now has > apply_proportional_protection() applied like get_scan_count() does, so > the MGLRU and traditional LRU behavior is now the same. > > Signed-off-by: T.J. Mercier Acked-by: Shakeel Butt