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Wed, 28 Oct 2026 14:21:36 -0700 (PDT) Date: Wed, 28 Oct 2026 17:21:36 -0400 From: Johannes Weiner To: "T.J. Mercier" Cc: roman.gushchin@linux.dev, muchun.song@linux.dev, Andrew Morton , Kairui Song , Qi Zheng , Shakeel Butt , 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 , 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-Queue-Id: 3D9B1140004 X-Stat-Signature: btmjffq7oumzd95gdzks9f9ror9537rp X-Rspamd-Server: rspam04 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: 1793222498-947799 X-HE-Meta: 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 h5v/LfJl 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 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 Great cleanup! Reviewed-by: Johannes Weiner