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Mon, 31 Mar 2025 18:02:57 +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 7X6MNdHY6mcLewAAD6G6ig (envelope-from ); Mon, 31 Mar 2025 18:02:57 +0000 Message-ID: <34504489-c260-45fa-8375-ac0f27b6677e@suse.cz> Date: Mon, 31 Mar 2025 20:02:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF Topic] Performance improvement for Memory Cgroups Content-Language: en-US To: Harry Yoo , Shakeel Butt Cc: linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org, Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Yosry Ahmed , Meta kernel team References: From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 7F89DC000D X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: hj31t9zntkoqyyp9tagac1b4in6au7nm X-HE-Tag: 1743444179-868466 X-HE-Meta: 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 qCP8Vgku vNEZfwgUQSgMTJ+8dmKs8HM3P3pRwRh4DbhzAekgN+Rr32H4EBxpiM8dhyztC5LotqC8Q/wzgqrnyEg6nPysKAi79SANLsoBLHkWdos/I31TDW3KfPJvw4tZz5fQjUxaxoXTiqnStqap3jfA9i6fTFpmiiLoFEhZ+IU6e2e6yP7MHYzrRR1oCFfs/oyvYryJXVToxXsFMK7VyJqIH4TnsXVlGA4nEHPDiz+EiPAbUOwoOqsSuFkr5MSNhRdmgrF+SN1CJfqSbe4KaPZNvfm8AyMdkLhWfV9kXfowt 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 3/20/25 07:22, Harry Yoo wrote: > On Tue, Mar 18, 2025 at 11:19:42PM -0700, Shakeel Butt wrote: > > For slab memory, I have an idea: > > Deferring the uncharging of slab objects on free until the CPU slab and > per-CPU partial slabs are moved to the per-node partial slab list > might be beneficial. > > Something like: > > 0. SLUB allocator defers uncharging objects if the slab the freed > objects belong to is the CPU slab or in the percpu partial slab > list. > > 1. memcg_slab_post_alloc_hook() does: > 1.1 Skips charging, if the object is already charged to the same > memcg and has not been uncharged yet. > 1.2 Uncharges the object if it is charged to a different memcg > and then charges it to current memcg. > 1.3 Charges the object if it's not currently not charged to any memcg. > > 2. deactivate_slab() and __put_partials() uncharges free objects > that were not uncharged yet before moving them to the per-node > partial slab list. > > Unless 1) we have tasks belonging to many different memcgs on each CPU > (I'm not an expert on the scheduler's interaction with cgroups, though), > or 2) load balancing migrates tasks between CPUs too frequently, > > many allocations should hit case 1.1 (Oh, it's already charged to the same > memcg so skip charging) in the hot path, right? > > Some experiments are needed to determine whether this idea is actually > beneficial. > > Or has a similar approach been tried before? I don't think so, it would have to be tried and measured. As I hinted in my sheaves slot, I doubt the step 0. above happens often enough. In step 2. you would have to walk the slabs' freelists to check if anything is charged, right?