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Tue, 14 Oct 2025 17:42:14 +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 Wl1yE3aL7mipNwAAD6G6ig (envelope-from ); Tue, 14 Oct 2025 17:42:14 +0000 Message-ID: <6f09edd2-2149-4854-9d2e-24b07bdccc75@suse.cz> Date: Tue, 14 Oct 2025 19:42:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/3] mm/page_alloc: Batch page freeing in free_frozen_page_commit Content-Language: en-US To: Joshua Hahn Cc: Andrew Morton , 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: <20251014131527.2682236-1-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: <20251014131527.2682236-1-joshua.hahnjy@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Stat-Signature: s7dprro4a8gzqcz63huhjogpr9hffwwn X-Rspam-User: X-Rspamd-Queue-Id: 4F81DA001B X-HE-Tag: 1760463736-856967 X-HE-Meta: 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 86TLULM9 ZsIxlKBHngTLzA+Ehjyhbbtw+/gN8QZdaJiKJNmaMqM+B8X9sGzopE250hwy5cGLyq2DCvP47jDPFp+0F0pGfFMny5GHdy7tekYsBZpNtwDUpxVia7ctto7m3uYEXnUE93eSTP/P8BELlJ7m4dnspH9TjuDnSS+0tijiOZW0F8e/c1H576ICHm2aWlqqGjnpivFyyDLOKVS0E0y3G7c1lvrzJ0evBgZ2HB1Q/Kc0Zv1hWnTO88i6GtcQ26RAKZBwn8fcFQ8B46ctaJ/wbicgrpKONycXo18z+0OHBvybCxBilu5Mz94X6fux97i0c5a6WvKf1pcRIWI3+2OVNB12R+E04UO1d0MTujNRg17nptAF2hhdlsPaRUCSfyasucwxky60n9BrencwopMyf5ajiaDzpSA== 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 15:15, Joshua Hahn wrote: > On Tue, 14 Oct 2025 11:38:00 +0200 Vlastimil Babka wrote: > >> On 10/13/25 21:08, 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 member. 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...] > >> > @@ -2861,15 +2871,47 @@ static void free_frozen_page_commit(struct zone *zone, >> > * Do not attempt to take a zone lock. Let pcp->count get >> > * over high mark temporarily. >> > */ >> > - return; >> > + return true; >> > } >> > >> > high = nr_pcp_high(pcp, zone, batch, free_high); >> > if (pcp->count < high) >> > - return; >> > + return true; >> > + >> > + to_free = nr_pcp_free(pcp, batch, high, free_high); >> > + if (to_free == 0) >> > + return true; > > Hello Vlastimil, thank you for your patience and review on this iteration! No problem! > >> > + to_free_batched = min(to_free, batch); >> > + free_pcppages_bulk(zone, to_free_batched, pcp, pindex); >> > + to_free -= to_free_batched; >> > + if (pcp->count >= high) { > > Here, I think I should change this in the next version to also just check > for the same condition in the while loop (i.e. to_free > 0 && pcp->count > 0) You're right, I missed that one. > The idea is that if we have another iteration, we will re-lock. Otherwise, we > can just ignore the case inside the if statement. I think if it is left as > a check for pcp->count >= high, then there will be a weird case for when > 0 < pcp->count <= high, where we continue to call free_pcppages_bulk but > do not re-lock. > > So unfortunately, I will have to check for the same condition of the > while loop in the if statement : -( I'll send a new version with the changes; > I don't expect there to be a drastic performance change, since I think the > early termination case would have only applied if there was a race condition > that freed the pcp remotely. Great!