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Mon, 27 Oct 2025 18:32:35 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id dK0THsO6/2iLCwAAD6G6ig (envelope-from ); Mon, 27 Oct 2025 18:32:35 +0000 Message-ID: <44066802-b505-4431-881d-371cf36f6d92@suse.cz> Date: Mon, 27 Oct 2025 19:32:35 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 15/17] memcg: Convert mem_cgroup_from_obj_folio() to mem_cgroup_from_obj_slab() Content-Language: en-US To: "Matthew Wilcox (Oracle)" , Andrew Morton Cc: Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , linux-mm@kvack.org References: <20251024204434.2461319-1-willy@infradead.org> <20251024204434.2461319-16-willy@infradead.org> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20251024204434.2461319-16-willy@infradead.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam01 X-Stat-Signature: 4niz7578kqcj4gftgnhcxgr4zthswhhm X-Rspam-User: X-Rspamd-Queue-Id: 2A57C20007 X-HE-Tag: 1761589957-145087 X-HE-Meta: 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 ErSFS8lF 1ZdlKzKh6D5mQjJcpxYZ4xxLycZ0u4wAoQKZsdYywKwOOGRAMz8FdsQhwjwRl+Zcw745vA69GjA6CmNz5bP6L+CkunvfwFZfRmAPuRMzOIQ6iL/AOs1GTg9JGd4UP5/LZYgwY+qN2mHffMJz0xA830z09pS+RCfhhM/gM66/rLBG6+uJQfZs0+JlDRkghAGViS7oahmVGismvr8YpStVzQG0GqPNmG9veEJF3GiUUdVCzDMl8Ty8BwbzSsvmD+Xi9FdgxhQdBe7Bu2VMZpQmySMZ2EidRWluhCO4p+krtZYI6VO/Shupbx/XiSbLa6G1/NJpO3HdutYk8ajimGf9L5kl23SXnXBVs5CIdt5RpqktDkDEYrDNyDaPw7q7mOB14qNKwk3Z2WTJ26vY= 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 10/24/25 22:44, Matthew Wilcox (Oracle) wrote: > In preparation for splitting struct slab from struct page and struct > folio, convert the pointer to a slab rather than a folio. This means > we can end up passing a NULL slab pointer to mem_cgroup_from_obj_slab() > if the pointer is not to a page allocated to slab, and we handle that > appropriately by returning NULL. > > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/memcontrol.c | 36 +++++++++++++----------------------- > 1 file changed, 13 insertions(+), 23 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 1a95049d8b88..c3ba53b40375 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2558,38 +2558,28 @@ static inline void mod_objcg_mlstate(struct obj_cgroup *objcg, > } > > static __always_inline > -struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, void *p) > +struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p) > { > /* > * Slab objects are accounted individually, not per-page. > * Memcg membership data for each individual object is saved in > * slab->obj_exts. > */ > - if (folio_test_slab(folio)) { > - struct slabobj_ext *obj_exts; > - struct slab *slab; > - unsigned int off; > - > - slab = folio_slab(folio); > - obj_exts = slab_obj_exts(slab); > - if (!obj_exts) > - return NULL; > + struct slabobj_ext *obj_exts; > + unsigned int off; > > - off = obj_to_index(slab->slab_cache, slab, p); > - if (obj_exts[off].objcg) > - return obj_cgroup_memcg(obj_exts[off].objcg); > + if (!slab) > + return NULL; > > + obj_exts = slab_obj_exts(slab); > + if (!obj_exts) > return NULL; > - } > > - /* > - * folio_memcg_check() is used here, because in theory we can encounter > - * a folio where the slab flag has been cleared already, but > - * slab->obj_exts has not been freed yet > - * folio_memcg_check() will guarantee that a proper memory > - * cgroup pointer or NULL will be returned. > - */ > - return folio_memcg_check(folio); The changelog should perhaps mention this removal so it doesn't give people pause. I think the comment describes an impossible scenario, you probably concluded the same. I'm not sure if it became impossible unnoticed at some point, or was bogus since the beginning. I'll pretend I did not try git blame that. > + off = obj_to_index(slab->slab_cache, slab, p); > + if (obj_exts[off].objcg) > + return obj_cgroup_memcg(obj_exts[off].objcg); > + > + return NULL; > } > > /* > @@ -2606,7 +2596,7 @@ struct mem_cgroup *mem_cgroup_from_slab_obj(void *p) > if (mem_cgroup_disabled()) > return NULL; > > - return mem_cgroup_from_obj_folio(virt_to_folio(p), p); > + return mem_cgroup_from_obj_slab(virt_to_slab(p), p); > } > > static struct obj_cgroup *__get_obj_cgroup_from_memcg(struct mem_cgroup *memcg)