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Fri, 6 Sep 2024 17:28:56 +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 b+uGIdg722Y4ZwAAD6G6ig (envelope-from ); Fri, 06 Sep 2024 17:28:56 +0000 Message-ID: Date: Fri, 6 Sep 2024 19:28:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] memcg: add charging of already allocated slab objects Content-Language: en-US To: Yosry Ahmed Cc: Shakeel Butt , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , David Rientjes , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Eric Dumazet , "David S . Miller" , Jakub Kicinski , Paolo Abeni , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Meta kernel team , cgroups@vger.kernel.org, netdev@vger.kernel.org References: <20240905173422.1565480-1-shakeel.butt@linux.dev> <572688a7-8719-4f94-a5cd-e726486c757d@suse.cz> 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+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Stat-Signature: hnbe3nf1aycr8rh86xw6u3d3f85hdzco X-Rspamd-Queue-Id: 9A90D2000A X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1725643738-29088 X-HE-Meta: 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 PrxIWnyg JbFwE69CGvlgRAW3X9V44/7Pyui6vyYnDd/Rpvk3KwHIWVnQzjA595A+ET+rCbsSlZpLgYDQTGIFQ3I4KYoRsJ4Pc2B0lZDeGeNbcXJnXfkM9av0LEwf40wH644vLy/UXdVlsxM/KNnww/IGJYmsX73SwiijZq8yAbkLCfCX4fhDsJBV3tI4lZLwGWmEUksPLn4Bsjk3ijdYwCnmoi53nyKde2DXoilYmEdhtr/V3jTbBFePprWFog0WO3Zga8DdBDtDw2v+WPR7tx3k/WvWmqDc4LPR64vAAjG+Uj3xDWcfp+Q2t1kqv6skjnqaLnQXX4c+fxL26GzHy8kjgdJrD9NMoQe6cFVJw/5zuxq1JIM8hF+U= 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 9/6/24 19:19, Yosry Ahmed wrote: > [..] >> I felt it could be improved more, so ended up with this. Thoughts? >> >> /** >> * kmem_cache_charge - memcg charge an already allocated slab memory >> * @objp: address of the slab object to memcg charge >> * @gfpflags: describe the allocation context >> * >> * kmem_cache_charge allows charging a slab object to the current memcg, >> * primarily in cases where charging at allocation time might not be possible >> * because the target memcg is not known (i.e. softirq context) >> * >> * The objp should be pointer returned by the slab allocator functions like >> * kmalloc (with __GFP_ACCOUNT in flags) or kmem_cache_alloc. The memcg charge > > Aren't allocations done with kmalloc(__GFP_ACCOUNT) already accounted? > Why would we need to call kmem_cache_charge() for those? AFAIU current_obj_cgroup() returns NULL because we're in the interrupt context and no remote memcg context has been set. Thus the charging is skipped. The patch commit log describes such scenario for network receive. But in case of kmalloc() the allocation must have been still attempted with __GFP_ACCOUNT so a kmalloc-cg cache is used even if the charging fails. If there's another usage for kmem_cache_charge() where the memcg is available but we don't want to charge immediately on purpose (such as the Linus' idea for struct file), we might need to find another way to tell kmalloc() to use the kmalloc-cg cache but not charge immediately... > I am assuming what you are referring to is kmalloc() allocations that > are not fulfilled from KMALLOC_NORMAL caches, but I am not sure how to > capture this here. > >> * behavior can be controlled through gfpflags parameter, which affects how the >> * necessary internal metadata can be allocated. Including __GFP_NOFAIL denotes >> * that overcharging is requested instead of failure, but is not applied for the >> * internal metadata allocation. >> * >> * There are several cases where it will return true even if the charging was >> * not done: >> * More specifically: >> * >> * 1. For !CONFIG_MEMCG or cgroup_disable=memory systems. >> * 2. Already charged slab objects. >> * 3. For slab objects from KMALLOC_NORMAL caches - allocated by kmalloc() >> * without __GFP_ACCOUNT >> * 4. Allocating internal metadata has failed >> * >> * Return: true if charge was successful otherwise false. >> */ >> >> >> > + >> >> > + /* Ignore KMALLOC_NORMAL cache to avoid circular dependency. */ >> >> >> >> Is it possible to point to the commit that has the explanation here? >> >> The one you pointed me to before? Otherwise it's not really obvious >> >> where the circular dependency comes from (at least to me). >> >> >> > >> > Not sure about the commit reference. We can add more text here. >> > Vlastimil, how much detail do you prefer? >> >> What about: >> >> /* >> * Ignore KMALLOC_NORMAL cache to avoid possible circular dependency >> * of slab_obj_exts being allocated from the same slab and thus the slab >> * becoming effectively unfreeable. >> */ >> >> >> > thanks, >> > Shakeel >>