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From: Shakeel Butt To: Johannes Weiner Cc: Andrew Morton , David Hildenbrand , Yosry Ahmed , Zi Yan , "Liam R. Howlett" , Usama Arif , Kiryl Shutsemau , Dave Chinner , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 6/7] mm: list_lru: introduce folio_memcg_list_lru_alloc() Message-ID: References: <20260318200352.1039011-1-hannes@cmpxchg.org> <20260318200352.1039011-7-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260318200352.1039011-7-hannes@cmpxchg.org> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 0893D18000E X-Stat-Signature: 5xbdt51gzwrygzcc4munhwbgya3ewpzp X-HE-Tag: 1773867726-671593 X-HE-Meta: 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 oFXM0e2V 9pIWaMEW5uthoiEPCmPFrBGS6UK3q60utdbe/toPcihkkqX2gvfn3uUv7Czh2gDJnvwp/8Pal05wA+4Hwhp/0/KKZAO9NRVpVYTrDC+ThftYYMaR+W/MLmoZDDq2zx0ADTn//BVhid32+3hQMb0Ugj1O8o0tDhAli1PykTvz7g+smed1Kgj1I2A9A4jmnRgjos7Ae1ByLWuVZVN/Q7TF71kau0T0pO6ewaHiveb35QF29+BYYMVPBZl6q92tbGeibFb2Gh922MpK0RNssq8jdxatVeKpkiYYuvqPLbDXGKGlM/5YiIjHAKvtCRcBJIENs/IZyHKkD741cpFU3xVxySWAMyQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 18, 2026 at 03:53:24PM -0400, Johannes Weiner wrote: > memcg_list_lru_alloc() is called every time an object that may end up > on the list_lru is created. It needs to quickly check if the list_lru > heads for the memcg already exist, and allocate them when they don't. > > Doing this with folio objects is tricky: folio_memcg() is not stable > and requires either RCU protection or pinning the cgroup. But it's > desirable to make the existence check lightweight under RCU, and only > pin the memcg when we need to allocate list_lru heads and may block. > > In preparation for switching the THP shrinker to list_lru, add a > helper function for allocating list_lru heads coming from a folio. > > Reviewed-by: David Hildenbrand (Arm) > Signed-off-by: Johannes Weiner Acked-by: Shakeel Butt