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b=sQHF9wmbR7uB2TkEtzgH81EVp6gsoWuhzfGCCboeFIcl1DKbRtUJEiAmdpdSvFuEb 0vWSSJF4hE1nqSM6y3rKl84LvWBFB8SJ33xlL3sjoATBlS3DNAz1C+EQ9oGoIL7ns3 tIOoZ6CdwNeU+P8gNBFaxhC1X5VZAVV9j8CNFVQc= Date: Tue, 1 Sep 2026 10:29:13 -0700 From: Andrew Morton To: Qinyun Tan Cc: Johannes Weiner , Michal =?ISO-8859-1?Q?Koutn=FD?= , Lance Yang , Qi Zheng , Roman Gushchin , Muchun Song , Dave Chinner , Baolin Wang , David Hildenbrand , Xunlei Pang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/list_lru: don't copy stale shrinker id from non-memcg-aware shrinkers Message-Id: <20260901102913.5c571bf153bc3830905c6770@linux-foundation.org> In-Reply-To: <20260901115104.2944996-1-qinyuntan@linux.alibaba.com> References: <20260901115104.2944996-1-qinyuntan@linux.alibaba.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-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 1B79612000C X-Stat-Signature: sba8o3j31zms5ka6r41r4rcqwf1jhkep X-HE-Tag: 1788283754-641455 X-HE-Meta: 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 AWythb+k uRVuOlP7E90HyWiJRWz+gmF78WxyCgF0y3vK1Puj/OKrNUUOyW149hqpo8N3UhjVVKUI2ZTvwOJcOfaXNZIBAtm+Hf/T1Wk4zvVOzqXBN+IRIirrQ4XOHJHzqLGqb7fuITqOmouIKsg8MkdJBvZuSYpCs3Ivgm0UIAffX+lfxI+PaxiJxMHOOgpkt+JQH6tLteHzF7abu3LGhcowLHIhxQ39TYa9CY7KrPOTFVICGkis5MRael9+gnCcwi5C5IT6gGuLhf+3UuZp9YLc2F/MKQ7QCaLZ2y22jvgvf+jK7dtv/IK7NiRMPUb38Ev3UgtLDc0yv2CwvENXr6QUNaZaYMHqIZKk4q+POAjB0JAUnd+HHUAlP3OUSluCBeOvdfFQRv0jG Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 1 Sep 2026 19:51:04 +0800 Qinyun Tan wrote: > With cgroup.memory=nokmem, shrinker_memcg_alloc() fails with -ENOSYS > for shrinkers without SHRINKER_NONSLAB, and shrinker_alloc() falls > back to a non-memcg-aware shrinker. On this fallback path, > shrinker->id is never assigned and keeps 0 from kzalloc(), which is a > valid id belonging to whichever memcg-aware shrinker registers first. > > __list_lru_init() copies shrinker->id unconditionally, so every > list_lru backed by such a fallback shrinker (thp-deferred_split, > zswap-shrinker, workingset shadow nodes, superblock lrus, ...) ends > up with lru->shrinker_id == 0 instead of -1. > > Under nokmem the list_lru collapses to the shared per-node lists, but > __list_lru_add() still calls set_shrinker_bit() against the memcg of > the added object. Most list_lru users are unaffected because their > objects resolve to a NULL memcg without kmem accounting, but the THP > deferred split queue holds user folios, which are charged regardless > of nokmem. Since no memcg-aware shrinker can register under nokmem, > shrinker_nr_max stays 0 and every memcg's shrinker_info has > map_nr_max == 0, so the first folio added by khugepaged triggers on > every boot: > > WARNING: mm/shrinker.c:212 at set_shrinker_bit+0x99/0xa0 > > On systems where a SHRINKER_NONSLAB shrinker (btrfs, xfs) did register > and expand the maps, there is no warning; instead bit 0 is set > spuriously for an unrelated shrinker. > > shrinker->id is only meaningful while SHRINKER_MEMCG_AWARE is set, > and all readers inside mm/shrinker.c already check the flag before > using the id. Make __list_lru_init() do the same and fall back to -1, > so set_shrinker_bit() is never reached with a bogus id. The stale > shrinker->id itself is left as is; cleaning that up is a separate > topic. Thanks. I'll queue this for test and review. > Fixes: 03375203e1da8 ("mm: do not allocate shrinker info with cgroup.memory=nokmem") Worth a cc:stable, I assume. > --- > > Verified on a machine booting with cgroup.memory=nokmem and > CONFIG_TRANSPARENT_HUGEPAGE=y: the warning fires once per boot from > khugepaged, disappears when nokmem is removed from the command line, > and no longer triggers with this fix applied and nokmem set. That's useful info. I'll move it into the changelog. Sashiko thinks there's a problem with cgroup_disable=memory as well: https://sashiko.dev/#/patchset/20260901115104.2944996-1-qinyuntan@linux.alibaba.com