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Mon, 22 Apr 2024 07:49:04 +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 lFFoDnAWJmbRcAAAD6G6ig (envelope-from ); Mon, 22 Apr 2024 07:49:04 +0000 Message-ID: Date: Mon, 22 Apr 2024 09:49:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] slub: introduce count_partial_free_approx() To: David Rientjes , Jianfeng Wang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux.com, akpm@linux-foundation.org, penberg@kernel.org References: <20240419175611.47413-1-jianfeng.w.wang@oracle.com> <20240419175611.47413-2-jianfeng.w.wang@oracle.com> <3e5d2937-76ab-546b-9ce8-7e7140424278@google.com> Content-Language: en-US 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: <3e5d2937-76ab-546b-9ce8-7e7140424278@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 61B5A100002 X-Stat-Signature: euhhdk5689hnaxazjdzm84f48xoep7su X-Rspam-User: X-HE-Tag: 1713772146-989610 X-HE-Meta: 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 C1kmOHUm HGR9BI7r8Wp8UWr0gwICRt+jG/DtTfHRIkJA90nCCixyForlFTKJregn4JK3Zvzooz6M4p01EVzRXrZurZ4BfrlbRxMiQSu4UJxM7Xzq9zPesi4qjKzX1r1qyuBkT5zlh8eO4JkX82OJNYxQLNEB7QpeEf7g32jVraBhhhVbkxwuDE91sZ9IecPOpOVH4IKJiwNfj35s2+8aZs/niriMlLhdOEN7k7bwmtqblRUahNmTUDFvt0kCDus/s1rZGfcBiqpzu2LpQzu5DBLvT6HzLwepYz9rI4e8WIrd6wbX89yY2hq89QWAjWNz8AeCnR84QJBtmPLet3ywj6lo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 4/20/24 2:18 AM, David Rientjes wrote: > On Fri, 19 Apr 2024, Jianfeng Wang wrote: > >> diff --git a/mm/slub.c b/mm/slub.c >> index 1bb2a93cf7b6..993cbbdd2b6c 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -3213,6 +3213,43 @@ static inline bool free_debug_processing(struct kmem_cache *s, >> #endif /* CONFIG_SLUB_DEBUG */ >> >> #if defined(CONFIG_SLUB_DEBUG) || defined(SLAB_SUPPORTS_SYSFS) >> +#define MAX_PARTIAL_TO_SCAN 10000 >> + >> +static unsigned long count_partial_free_approx(struct kmem_cache_node *n) >> +{ >> + unsigned long flags; >> + unsigned long x = 0; >> + struct slab *slab; >> + >> + spin_lock_irqsave(&n->list_lock, flags); >> + if (n->nr_partial <= MAX_PARTIAL_TO_SCAN) { >> + list_for_each_entry(slab, &n->partial, slab_list) >> + x += slab->objects - slab->inuse; >> + } else { >> + /* >> + * For a long list, approximate the total count of objects in >> + * it to meet the limit on the number of slabs to scan. >> + * Scan from both the list's head and tail for better accuracy. >> + */ >> + unsigned long scanned = 0; >> + >> + list_for_each_entry(slab, &n->partial, slab_list) { >> + x += slab->objects - slab->inuse; >> + if (++scanned == MAX_PARTIAL_TO_SCAN / 2) >> + break; >> + } >> + list_for_each_entry_reverse(slab, &n->partial, slab_list) { >> + x += slab->objects - slab->inuse; >> + if (++scanned == MAX_PARTIAL_TO_SCAN) >> + break; >> + } >> + x = mult_frac(x, n->nr_partial, scanned); >> + x = min(x, node_nr_objs(n)); >> + } >> + spin_unlock_irqrestore(&n->list_lock, flags); >> + return x; >> +} > > Creative :) > > The default value of MAX_PARTIAL_TO_SCAN seems to work well in practice > while being large enough to bias for actual values? > > I can't think of a better way to avoid the disruption that very long > partial lists cause. If the actual value is needed, it will need to be > read from the sysfs file for that slab cache. > > It does beg the question of whether we want to extend slabinfo to indicate > that some fields are approximations, however. Adding a suffix such as > " : approx" to a slab cache line may be helpful if the disparity in the > estimates would actually make a difference in practice. I'm afraid that changing the layout of /proc/slabinfo has a much higher chance of breaking some consumer, than the imprecision due to approximation has. So I would rather not risk it. > I have a hard time believing that this approximation will not be "close > enough" for all practical purposes, given that the value could very well > substantially change the instant after the iteration is done anyway. > > So for that reason, this sounds good to me! > > Acked-by: David Rientjes > >> + >> static unsigned long count_partial(struct kmem_cache_node *n, >> int (*get_count)(struct slab *)) >> { >> @@ -7089,7 +7126,7 @@ void get_slabinfo(struct kmem_cache *s, struct slabinfo *sinfo) >> for_each_kmem_cache_node(s, node, n) { >> nr_slabs += node_nr_slabs(n); >> nr_objs += node_nr_objs(n); >> - nr_free += count_partial(n, count_free); >> + nr_free += count_partial_free_approx(n); >> } >> >> sinfo->active_objs = nr_objs - nr_free;