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Fri, 12 Apr 2024 07:48:41 +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 FQ30AlnnGGZicAAAD6G6ig (envelope-from ); Fri, 12 Apr 2024 07:48:41 +0000 Message-ID: <38ef26aa-169b-48ad-81ad-8378e7a38f25@suse.cz> Date: Fri, 12 Apr 2024 09:48:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] slub: limit number of slabs to scan in count_partial() Content-Language: en-US To: "Christoph Lameter (Ampere)" , Jianfeng Wang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, junxiao.bi@oracle.com References: <20240411164023.99368-1-jianfeng.w.wang@oracle.com> 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-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: E81724000B X-Stat-Signature: yxphmxro1neg5g6uanok39aq84b1hq34 X-HE-Tag: 1712908123-230712 X-HE-Meta: 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 +lOrki9V v1a5MY6han0eS+wIdxY3Z+TYMkLLE1wfmF3SeiftRAJPrHl0A/WL2dRcFIWck5MJcBS0rfTclzgo5E5XPfrM50AmInntOTuEyHHhENlEZiiKE+BpxQVF0IhjKa6SIAyk7k0LtKbywLe6zKIexfMLK6LltwnG/MQ6weA/ueVRTe8OqxzKscp76GjU6NJkjR14oSEUHCdCZF3Xj9/wgNxthKYREXinvZ9mdmDBkShcI3ypWsS2DJdNcOSRsAPAD0ztHQGQ85vzLTWteDr2tgEVLDOwVOI+9f1o8qSRlCWVTmwfMJs62Y8EdhG0cpw== 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 4/11/24 7:02 PM, Christoph Lameter (Ampere) wrote: > On Thu, 11 Apr 2024, Jianfeng Wang wrote: > >> So, the fix is to limit the number of slabs to scan in >> count_partial(), and output an approximated result if the list is too >> long. Default to 10000 which should be enough for most sane cases. > > > That is a creative approach. The problem though is that objects on the > partial lists are kind of sorted. The partial slabs with only a few > objects available are at the start of the list so that allocations cause > them to be removed from the partial list fast. Full slabs do not need to > be tracked on any list. > > The partial slabs with few objects are put at the end of the partial list > in the hope that the few objects remaining will also be freed which would > allow the freeing of the slab folio. > > So the object density may be higher at the beginning of the list. > > kmem_cache_shrink() will explicitly sort the partial lists to put the > partial pages in that order. > > Can you run some tests showing the difference between the estimation and > the real count? Maybe we could also get a more accurate picture by counting N slabs from the head and N from the tail and approximating from both. Also not perfect, but could be able to answer the question if the kmem_cache is significantly fragmented. Which is probably the only information we can get from the slabinfo vs . IIRC the latter is always accurate, the former never because of cpu slabs, so we never know how many objects are exactly in use. By comparing both we can get an idea of the fragmentation, and if this change won't make that estimate significantly worse, it should be acceptable.