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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1t1kVS-0000000D0QW-44Fx; Fri, 18 Oct 2024 10:46:55 +0000 Date: Fri, 18 Oct 2024 11:46:54 +0100 From: Matthew Wilcox To: David Hildenbrand Cc: linux-mm@kvack.org, Yu Zhao Subject: Re: Next steps towards shrinking stuct page Message-ID: References: <399f12d4-b01d-40bd-aba7-e3c565fbd8cb@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <399f12d4-b01d-40bd-aba7-e3c565fbd8cb@redhat.com> X-Rspamd-Queue-Id: ECFB740018 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: xax5dc9bigwcs6qm8rea4ggitzx6tgjo X-HE-Tag: 1729248401-66771 X-HE-Meta: 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 TqLxMzrX o+0YnhVHMEOMPTtv/0bVgtaqz9enu4q8ID7EyisPJ5g5qd6103CWe96UVmcuvYOP560voqtawIC8s1jFoLla/jE4zLB3i6ViF6wW9fuZ3djU75E8jAjBPsw58D1rRjQ77aznsBKbQ/5M5GB0aptoRVBj5sqv5KxFrdnPbUPSPeEMqeUVzB/tDOGfvX4T1twpk1sCIpCYe5hWWcLPgSQE3JpboNQ1mqxkC2Lhw 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 Tue, Oct 08, 2024 at 04:16:39PM +0200, David Hildenbrand wrote: > > > > 4. Make sure that we're good with memcg_data. I think we are (it's only > > used in folios and slabs today, I _think_), but it'll be good to be > > sure. Someone who understands memcg better than I do can probably find > > some stuff to clean up. > > Last time I looked at this (1month ago), I had the same impression. I took a shot at this. The problem is mm/page_alloc.c: __alloc_pages_noprof: if (memcg_kmem_online() && (gfp & __GFP_ACCOUNT) && page && unlikely(__memcg_kmem_charge_page(page, gfp, order) != 0)) { __free_pages(page, order); page = NULL; } I think someone (maybe Yosry?) tried to explain this problem to me at LSFMM, but I didn't understand. Most of the places that use GFP_KERNEL_ACCOUNT are either page tables or kmalloc/kvmalloc. But I think we're going to need a new memdesc type for accounted memory. struct accounted_mem { unsigned long flags; struct obj_cgroup *objcg; }; (we'll be able to drop MEMCG_DATA_* once we have the memdesc type, but we need to keep it until we're there). So I guess that's my next step -- adding: struct accounted_mem { unsigned long flags; unsigned long padding[5]; unsigned int padding2[2]; unsigned long objcg; }; and the various assertions that objcg & flags occupy the same bytes in accounted_mem as they do in page, until we separate them entirely.