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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1t1mLU-0000000DB4C-2GZU; Fri, 18 Oct 2024 12:44:44 +0000 Date: Fri, 18 Oct 2024 13:44:44 +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> <30452c92-2fcd-4931-b58f-4d37713c84bc@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <30452c92-2fcd-4931-b58f-4d37713c84bc@redhat.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D01DB40014 X-Stat-Signature: fk13hj3dkyeeyryft5h4jr8i9dq6of9q X-Rspam-User: X-HE-Tag: 1729255477-187486 X-HE-Meta: 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 P64gnSXx vReAARbgqj/lrqZRZjGF9VWOH2uJTP2V0a7L0VCQ1NNdaWRdXV1HJINyF+90j5SX4YUqQmvTIlTkUISXQs6DcrvpG4ugTBibKZ+u6grmO/hKrt34CvuSYmMzb3uxcC3A1XAamiRNMK0wFX9tLu9+yAMg7A7G1m9Fj3+UfFDzefKyOPv9BwR5qDgkVNNT1MBvPU5kfjB+GEBvYSE8vDQJG959zMvguQkaTcuTW 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 Fri, Oct 18, 2024 at 01:07:43PM +0200, David Hildenbrand wrote: > On 18.10.24 12:46, Matthew Wilcox wrote: > > 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; > > } > > > > Right, I recall that we are only touching the first page. IIRC, it's not > necessarily a compound page. That fits with how split_page_memcg() operates. > > struct accounted_mem { > > unsigned long flags; > > struct obj_cgroup *objcg; > > }; [...] > > 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. > > But how to do that without a compound page? The first step is just an exercise in typing. We'll use the exact same bits for the exact same purpose, just eliminating all references to page->memcg_data. Later, we'll progress to separately allocating a 16-byte accounted_mem.