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Mon, 19 Feb 2024 10:17:53 +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 rYP0B9Eq02UWIgAAD6G6ig (envelope-from ); Mon, 19 Feb 2024 10:17:53 +0000 Message-ID: Date: Mon, 19 Feb 2024 11:17:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] slub: avoid scanning all partial slabs in get_slabinfo() Content-Language: en-US To: Chengming Zhou , David Rientjes , Jianfeng Wang Cc: cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240215211457.32172-1-jianfeng.w.wang@oracle.com> <6b58d81f-8e8f-3732-a5d4-40eece75013b@google.com> <5cf40e33-d1ae-4ac9-9d01-559b86f853a8@bytedance.com> From: Vlastimil Babka In-Reply-To: <5cf40e33-d1ae-4ac9-9d01-559b86f853a8@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spamd-Bar: + X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 0BCF94000A X-Stat-Signature: h4qgchadjdn7mbpanqtz58pf8ktn4oua X-HE-Tag: 1708337876-886748 X-HE-Meta: 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 ZQvRJdOO 6MsAaYgDKbtX3il+kCy+AOBqFx+c8kY7aDgrQz1TxTWAr6ln3c0P1A/8NH6bMuyrkKKFFvJreO10hk4KM79dStsv5Zw== 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 2/19/24 10:29, Chengming Zhou wrote: > On 2024/2/19 16:30, Vlastimil Babka wrote: >> On 2/18/24 20:25, David Rientjes wrote: >>> On Thu, 15 Feb 2024, Jianfeng Wang wrote: >>> >>>> When reading "/proc/slabinfo", the kernel needs to report the number of >>>> free objects for each kmem_cache. The current implementation relies on >>>> count_partial() that counts the number of free objects by scanning each >>>> kmem_cache_node's partial slab list and summing free objects from all >>>> partial slabs in the list. This process must hold per kmem_cache_node >>>> spinlock and disable IRQ. Consequently, it can block slab allocation >>>> requests on other CPU cores and cause timeouts for network devices etc., >>>> if the partial slab list is long. In production, even NMI watchdog can >>>> be triggered because some slab caches have a long partial list: e.g., >>>> for "buffer_head", the number of partial slabs was observed to be ~1M >>>> in one kmem_cache_node. This problem was also observed by several > > Not sure if this situation is normal? It maybe very fragmented, right? > > SLUB completely depend on the timing order to place partial slabs in node, > which maybe suboptimal in some cases. Maybe we could introduce anti-fragment > mechanism like fullness grouping in zsmalloc to have multiple lists based > on fullness grouping? Just some random thoughts... :) Most likely that's wouldn't be feasible. When freeing to a slab on partial list that's just a cmpxchg128 (unless the slab become empty) and additional list manipulation to maintain the grouping would kill the performance.