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Tue, 14 Oct 2025 20:45:07 +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 CuHWDlO27mgMZAAAD6G6ig (envelope-from ); Tue, 14 Oct 2025 20:45:07 +0000 Message-ID: <20564b23-a3eb-4282-acec-be8913a84daa@suse.cz> Date: Tue, 14 Oct 2025 22:45:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 3/3] mm/page_alloc: Batch page freeing in free_frozen_page_commit Content-Language: en-US To: Joshua Hahn , Andrew Morton Cc: Chris Mason , Kiryl Shutsemau , Brendan Jackman , Johannes Weiner , Michal Hocko , Suren Baghdasaryan , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com References: <20251014192827.851389-1-joshua.hahnjy@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: <20251014192827.851389-1-joshua.hahnjy@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: hmzdmjnjwf8bhjre97aonj35r9nzymxw X-Rspamd-Queue-Id: 80C0540003 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1760474710-70180 X-HE-Meta: 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 XQYLb+qE MthvndwAoCfiBfGk9ZVrgT6ho62rIG/Pn+keGS/cr73xoe0o7kXigx6JB5z1/yosHBHKgZyPq8VRnycPIaql6Vy4xstfKI0/g9ei4eYx2KZoISAtoeWsF3uNqLXt4fcyB4Ifk4P4NErRmYLu1EdIEk4CRaTCpcKYhLHLQSr1bpgze9dJntW1TFAD/gXa/mdsVjjuNlERT/CTlnrBkVeR6k7PbZShIOmt7Fe4383vp16CBwAOlp9oO9xiLTsxBiETi5CE9hUFMY4YjWIobCEVQ7OlzLPpq/eHE8sMUI6vA5G9TK6j7q1Ld5GRf5Nx9Z2X+cUUY6fNYxvuyREByuvWFwGJZopZbmaYeoxsM0JfVA8M/Dw9/E7ZtVP1v9b7DeJvptwpLiGypiXacRjQU2ySeoq4zP60NBf6elrDhuPndOm9g6OgI5eyr+ks0lFAj6vcElZw0JAAgskI/ARksSUZhydp/tw== 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 10/14/25 21:28, Joshua Hahn wrote: > On Tue, 14 Oct 2025 07:50:10 -0700 Joshua Hahn wrote: > >> Before returning, free_frozen_page_commit calls free_pcppages_bulk using >> nr_pcp_free to determine how many pages can appropritately be freed, >> based on the tunable parameters stored in pcp. While this number is an >> accurate representation of how many pages should be freed in total, it >> is not an appropriate number of pages to free at once using >> free_pcppages_bulk, since we have seen the value consistently go above >> 2000 in the Meta fleet on larger machines. >> >> As such, perform batched page freeing in free_pcppages_bulk by using >> pcp->batch. In order to ensure that other processes are not starved of the >> zone lock, free both the zone lock and pcp lock to yield to other threads. >> >> Note that because free_frozen_page_commit now performs a spinlock inside the >> function (and can fail), the function may now return with a freed pcp. >> To handle this, return true if the pcp is locked on exit and false otherwise. >> >> In addition, since free_frozen_page_commit must now be aware of what UP >> flags were stored at the time of the spin lock, and because we must be >> able to report new UP flags to the callers, add a new unsigned long* >> parameter UP_flags to keep track of this. > > [...snip...] > > Hello Andrew, I hope you are doing well! I was wondering if you could help > adding this as a fixlet for the patch I am writing this reply to. Vlastimil > kindly pointed out that they should never go negative, so checking for > 0-ness should be sufficient and more readable than the <= checks. > > I think it is OK to leave the changelog in 0/3 unchanged, since it will not go > into the commit history and Vlastimil has already left a correction. But > please let me know if you would like me to add a correction for that as well. > > Thank you as always, for your help! I hope you have a great day! > Joshua > > ... > > Since to_free and pcp->count cannot become negative, make the checks into an > equality check instead. > > Signed-off-by: Joshua Hahn For the patch with this fixup: Reviewed-by: Vlastimil Babka Thanks! > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 6d544521e49c..fd46a982ce3c 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2884,7 +2884,7 @@ static bool free_frozen_page_commit(struct zone *zone, > free_pcppages_bulk(zone, to_free_batched, pcp, pindex); > to_free -= to_free_batched; > > - if (to_free <= 0 || pcp->count <= 0) > + if (to_free == 0 || pcp->count == 0) > break; > > pcp_spin_unlock(pcp);