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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vJe0s-000000086x7-3brw; Thu, 13 Nov 2025 20:33:50 +0000 Date: Thu, 13 Nov 2025 20:33:50 +0000 From: Matthew Wilcox To: Shakeel Butt Cc: Vlastimil Babka , Johannes Weiner , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , linux-mm@kvack.org, Michal Hocko , Muchun Song , cgroups@vger.kernel.org Subject: Re: [PATCH v4 14/16] memcg: Convert mem_cgroup_from_obj_folio() to mem_cgroup_from_obj_slab() Message-ID: References: <20251113000932.1589073-1-willy@infradead.org> <20251113000932.1589073-15-willy@infradead.org> <20251113161424.GB3465062@cmpxchg.org> <45ea66a3-bf8b-4c12-89cd-d15ba26763fa@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: meqr8qog8hs8aqczinf9tzue1qdzdn17 X-Rspam-User: X-Rspamd-Queue-Id: 66DE7180009 X-Rspamd-Server: rspam01 X-HE-Tag: 1763066036-626678 X-HE-Meta: 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 DGI8FWPa CyQKw9eDCUehO8OWw39mHFrRUFqVEPa+BfF0zfXDSIsbiQ2XJQMpoO/ktreYfpdY5ecMC79tx7j+SdBkoxPm18JFlTIqjs84yJQvojPecsApeqLPPLXu89H/zmFeqY0vtWNt50oHt5eCVf156Hn6SMKyCYV+d87fVdakCw+5O2UEtYlHZEH14D3sI0YspyFquMwUJTYFkE+mmnpDLm/S4WH4E5ldGV+OCBWulVveKr8rCvp5ccRA9jDcL//T3IDiokbMTAtng47PLLg+wwvN6/bChOxCA90lnK4ohbB+GR/xVqIA= 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 Thu, Nov 13, 2025 at 11:42:01AM -0800, Shakeel Butt wrote: > On Thu, Nov 13, 2025 at 05:28:59PM +0100, Vlastimil Babka wrote: > > > E.g. !vmap kernel stack pages -> mod_lruvec_kmem_state -> mem_cgroup_from_obj_slab > > > > > > How about: > > > > > > if ((slab = virt_to_slap(p))) > > > return mem_cgroup_from_obj_slab(slab, p); > > > return folio_memcg_check(virt_to_folio(p), p); > > > > page_memcg_check() maybe instead? we shouldn't get a tail page here, no? > > Do you mean page_memcg_check(virt_to_page(p), p)? But virt_to_page(p) > can return tail page, right? Only if it's legitimate to call mod_lruvec_kmem_state() with "a pointer to somewhere inside the object" rather than "a pointer to the object". For example, it's legitimate to call copy_to_user() with a pointer somewhere inside the object, so the usercopy code has to handle that case. But it's only legitimate to call kfree() with a pointer that's at the start of an object, so kfree() can cheerfully BUG_ON() PageTail(virt_to_page(p)).