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b=O05SGGAdRPGrz0Iz+7XgwlSFs3F5RnNc0orTk5KU9yz8aeD27Z+fCAQ3JX0fHfAEj xCod+mWvLIGO/opeBlR1JATMb1O+8IRDeeSegYbMSJR+L9p5b2Ub+H2SkHHpUfRdLI qy6BtR30pEznfw5G2Iuf6kFVI7MNCf+iTXB84EaRmILGvGIc5FPXdkP9Ff8ytneID7 gIFmvbA+UcB/J23fjfmlJoNt24rtTwQzOs/B4UV5CiExvTA4rmgoVawucc8weY5wUN Hpb6skjv+czEk0J2VNgwAc9cIVAlFId7X9MaNUxsJqVfimJLnn0UL4iyyFxOuckQTi 5VOJUhZcIujVg== Message-ID: <4d9ebf64-e3b4-4b6c-9576-e8be59193f80@kernel.org> Date: Tue, 15 Sep 2026 09:10:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] mm/slub: reduce list_lock contention with slab parking Content-Language: en-US To: Hao Li Cc: harry@kernel.org, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pedro Falcato References: <20260824122004.3652-1-hao.li@linux.dev> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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 BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: uqrk8zd7aa9kntiuww691xfsw118sngn X-Rspamd-Queue-Id: 1DCBE140007 X-Rspamd-Server: rspam07 X-HE-Tag: 1789456226-717858 X-HE-Meta: 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 t1ods44r HPBvu8D2PRdhaMvyycmqpYqdVoVHFOL3wKSI+hhywP4SeXB4K3b+S2HemWhnCAacVPfUDUZFm1YzGg4BK5MxjLFNlDVzOF+r9PG+s99PbS9LmlKqO/HAQ20S15/tSMbZPeapMwEBb9EsD3X30FQHmP8vH7UMx0yD/UEjLfMfRo9Pr1czevCqApW+ex/2J5zsm5bLgn12m6BfBWtBFXnM7Qe7O8xKIVkul89wzCwxYC+oN88ukxdN0wpzoMJ1WeNhQnzsg4oNsW9x2qUNKh5emMhpOgxD92HNgVxqn3ORkyuIcVHXb+2PCpRRAjw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/11/26 13:24, Hao Li wrote: > On Mon, Sep 07, 2026 at 03:44:08PM +0200, Vlastimil Babka (SUSE) wrote: >> On 8/24/26 14:19, Hao Li wrote: >> > >> > Detailed data >> > ------------- >> > >> > metric before after delta change >> > ========================================================================================== >> > alloc_fastpath 155,417 168,534 13,117 +8.44% >> > alloc_slab 55,679,646 26,702,510 -28,977,136 -52.04% >> >> It's interesting that this is reduced so much. Is it because parked slabs >> cause more slabs to stay around for reuse, despite they are unparked >> immediately when trying to allocate/refill? That seems odd? > > Yeah, it does look counter-intuitive at first glance. My understanding is that > the parking mechanism helps by bypassing the partial list spinlock, allowing > partial slabs to be parked onto the llist locklessly at any point. Because of > this, the refill path gets to see and reuse more partial slabs instead of > having to allocate fresh ones so frequently. Hmm that's an interesting effect, surprisingly large if true. Because the slabs we'd be parking are transitioning from full, there would be most often just a single free object to reuse? >> >> > alloc_slowpath 0 0 0 +0.00% >> > barn_get 2,715 2,771 56 +2.06% >> > barn_get_fail 2 0 -2 -100.00% >> > barn_put 2,715 2,770 55 +2.03% >> > barn_put_fail 1,370,488,457 1,668,257,974 297,769,517 +21.73% >> > cmpxchg_double_fail 3,827,935 549,427 -3,278,508 -85.65% >> > free_add_partial 1,684,340,964 2,161,921,625 477,580,661 +28.35% >> > free_fastpath 31,766 32,979 1,213 +3.82% >> > free_rcu_sheaf 43,855,689,417 53,384,314,553 9,528,625,136 +21.73% >> >> This metric (and others with similar numbers) should not be affected by the >> change. Does it mean the benchmark has a fixed time to run, but manages to >> do more work in that time thanks to the increased throughput? > > Exactly! In fact, the increase in free_rcu_sheaf matches the throughput gain > almost 1:1. A ~21% increase in throughput naturally translates to ~21% more object > allocations and frees. Ack!