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Mon, 15 Dec 2025 14:30:49 +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 vOf9BJkbQGkvIwAAD6G6ig (envelope-from ); Mon, 15 Dec 2025 14:30:49 +0000 Message-ID: Date: Mon, 15 Dec 2025 15:30:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] slub: keep empty main sheaf as spare in __pcs_replace_empty_main() Content-Language: en-US To: Hao Li , akpm@linux-foundation.org, harry.yoo@oracle.com, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251210002629.34448-1-haoli.tcs@gmail.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+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20251210002629.34448-1-haoli.tcs@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam02 X-Stat-Signature: 4a6yf5cg6ukzzmp49q3685zhcnsdd38x X-Rspam-User: X-Rspamd-Queue-Id: F00D04001E X-HE-Tag: 1765809050-368479 X-HE-Meta: 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 gAOiyL65 qWR/CddHZYclTtzzXwjNN6EY6hlcEun0nkWQqx5V6oc1QjHhq8JI2gW5mB8PdrHE/EuYwUaiQ/ElUEDce3WVmrdfpGsViYutBYireysxxMkGjgLJLQakYwoaCmefvrIfywte0TEhXuIXOwtok8mqagQ8j4WAaplH5CAnpqixPEzauss1ybVViKiSq9FmK1kNSIP68CUAncUeWe+0X5JoYeS4nkjcmYiQ7K+h3wl8wEYGbgXcnS9kmFzDij0h/euBYS+Tatq0yPQ07zQ8CLC4SASlPuHMhifpohImO1UHh3RloOGZxqDqdNbTjYKgXLz4dhPbnMFv1Q3RHlIeFYNNBeaKUBWnjiIMLmpmrEE0V/E31zcCWrw/Uk2iBYxa7ec3ECsQ840bdk3qc/2pQrWPlZV4JybYzdV5Zy/EY/465RqSnits= 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 12/10/25 01:26, Hao Li wrote: > From: Hao Li > > When __pcs_replace_empty_main() fails to obtain a full sheaf directly > from the barn, it may either: > > - Refill an empty sheaf obtained via barn_get_empty_sheaf(), or > - Allocate a brand new full sheaf via alloc_full_sheaf(). > > After reacquiring the per-CPU lock, if pcs->main is still empty and > pcs->spare is NULL, the current code donates the empty main sheaf to > the barn via barn_put_empty_sheaf() and installs the full sheaf as > pcs->main, leaving pcs->spare unpopulated. > > Instead, keep the existing empty main sheaf locally as the spare: > > pcs->spare = pcs->main; > pcs->main = full; > > This populates pcs->spare earlier, which can reduce future barn traffic. > > Suggested-by: Vlastimil Babka > Signed-off-by: Hao Li > --- > > The Gmail account(haoli.tcs) I used to send v1 of the patch has been > restricted from sending emails for unknown reasons, so I'm sending v2 > from this address instead. Thanks. > > mm/slub.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/slub.c b/mm/slub.c > index a0b905c2a557..a3e73ebb0cc8 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5077,6 +5077,11 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, > */ > > if (pcs->main->size == 0) { > + if (!pcs->spare) { > + pcs->spare = pcs->main; > + pcs->main = full; > + return pcs; > + } > barn_put_empty_sheaf(barn, pcs->main); > pcs->main = full; > return pcs; Thanks, LGTM. We can make it smaller though. Adding to slab/for-next adjusted like this: diff --git a/mm/slub.c b/mm/slub.c index f21b2f0c6f5a..ad71f01571f0 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5052,7 +5052,11 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, */ if (pcs->main->size == 0) { - barn_put_empty_sheaf(barn, pcs->main); + if (!pcs->spare) { + pcs->spare = pcs->main; + } else { + barn_put_empty_sheaf(barn, pcs->main); + } pcs->main = full; return pcs; }