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Howlett" , Mike Rapoport , Qi Zheng , Shakeel Butt , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , Dev Jain , Usama Arif , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20261102093939.3340540-1-kas@kernel.org> <20261102093939.3340540-2-kas@kernel.org> 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-Rspamd-Queue-Id: 84EB3C0013 X-Rspamd-Server: rspam12 X-Stat-Signature: of5mm1r9o53s8g568uq1j3fqh4ksr4b3 X-Rspam-User: X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1794589388-433208 X-HE-Meta: U2FsdGVkX1/9dyb9b3n6F6UTI29gWsRxuAHvG00HE8tCR7MFjLtrCqu7lgNphhRNtAC8SDF52JzvjQ0LIaPTEbSJWaTjw+xFKeFsGrh9I4zsuE1bOiqsY2Jav+pM3Zc/Epq6jfn80KGmoOUgwLxdVSMk/PCrCg8V5dgvuRpGCFNGZhzMaE1NnSjaBsYfFIpogePdSoKnQl2vuikRqL1gIpUxCG9TPTv90uwpdLgLl0tM3DJ48AOFqJOVERvWXK0xqI5wA1ZPT3l6kb1HrrWLd90nMVU6fOx1F3eA6xkYob5ywhQqbVfXRcUV+UB+1xVXyEONh4C3Il4Lv6cnshK3eXzqLDwsvyrmQVnc6WSMX2AIPlfAmLupvLaUQBn6fPJSyeWVm81DhB3f6aSiPJ28xjvwNMerZtI5XNRKYzat4f0hE+gslZixq4Acp2Z9WYar7zaxWRWVAr+PmL/Jg+bl7hVlytu3FV8zH/KCgIuHX6m5wPwA9evx1qBmeseRbTh4rFFj0dr/lIrMqQliQp9oITN7KYqfqQGwwxFQfV69aCBUFGhtUeTa51LvfpjA2Ttof/1RUPxRzOwCr5ZxIXbFu42jkomf9EHbdJy2VVPFtrZJ1WK/KoNBfoa99bgxR+ZbEHXNi0Afeu880Or1eYMny58oXz3anoTXbF+2et39HGrBF/VlzlUOu3ZiGq2ZyGkSkgx6ba3fn7looU5jXvMQdZuCHdl8wv/XJvYNnzwmgBYHJwmnz8m4hAvlSEr5WvGUIg7FA/IzMVamRFdOpGMNNYRzV5byuQp2Y8bDOog7UFoT5qZGJnPSRUf1NMghIWqT9XocTNkaeTuw5nJF9u1yLke4fYeW4/JTLhO3X5rC2veQ0+9T0+TdbLQx6UNm0R9fb2Yyk4gBBIEyMd0QpGCTJC2NIGgeWHHYNF0y2AZYydKGaJSAdZgoh9J2D/2PHXDWHE7Llu/5/zlSHnfymGT 68cd3eBd PvOcTs89yH2PXAQTk2B3XaC9dt0ZViqOszHlPAh/3keSkBdaxeBbfABQyjIjxFa6g0KpnKLFW/ONVr7uaPUjGcrRN/dCZwF5x/PTfbbKUNa6iSlCUflaBjeBEiWxGeidXLt+VwNaboBAu5pP7rzPcdmcuEd0ieXF5yPwDYZiodAxgfb4/IBtaVPyLg2hnkXOp6sHYlQYVIIB6JREofBX8XwWx9fEO87WA8np43yHE9/6krxdL8P2MSWGA7vK798DSlOt0jdTG4dsS+SGseKGUQTdmBidSI7iRQ6rr+8MElK4FQszLhzLDfI/GHHNLlQM2MQrOmyI43qLl03gSX47j9b2WVQOdUjYXlSCYJa/PIU7wHnqVRQgJHm/T0nTdr3X/pW522yqef8AAsgbtZI3AdAR1hBPPp92OKVdQ8yVEwxrjVGdMHjt6y932AkqqZUqhjQ/FQKrClZAJrOo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/11/26 20:49, Kiryl Shutsemau wrote: > On Thu, Nov 05, 2026 at 05:06:39PM +0000, Harry Yoo wrote: >> On Mon, Nov 02, 2026 at 09:39:34AM +0000, Kiryl Shutsemau (Meta) wrote: >> > The high-order check in __zone_watermark_ok() accepts a free page of any >> > migratetype. Under ALLOC_NOFRAGMENT, a request below pageblock_order can >> > only take a page of its own migratetype or claim a whole free block, so >> > the check can pass when the allocation cannot succeed. >> > >> > Telling those apart needs the request's migratetype, but not every check >> > wants them told apart. A check whether an allocation can be served now >> > has to count only the pages it can take. >> > >> > A check whether there is enough free memory counts every migratetype: >> > kswapd and kcompactd balancing a zone, order-0 thresholds, the >> > slowpath's forecast whether reclaim and compaction can still make >> > progress. Reclaim and compaction work across migratetypes to free whole >> > pageblocks. >> >> nit: perhaps we could make the changelog above bit more concise. >> >> I think the necessary bit here is "With defrag_mode, allocations cannot >> steal a page from pageblocks of other migrate type, thus >> __zone_watermark_ok() needs to take that into account." > > > It is ALLOC_NOFRAGMENT, not defrag_mode: Normal zone allocations get it > on the first attempt when DMA32 is populated, with defrag_mode off. And > such an allocation can still claim a whole free pageblock of another > migratetype. > > But fair, it can be shorter. A tighter version is below; it also says > why kcompactd passes MIGRATE_MOVABLE. > >> nit: maybe let's set cc.migratetype and pass it? > > The value is not read there: __zone_watermark_ok_mt() uses the > migratetype only under ALLOC_NOFRAGMENT, and kcompactd never passes it. > kcompactd_node_suitable() makes the same call and has no compact_control > to take it from. > > Thanks for the review. > > The new changelog: > > The high-order check in __zone_watermark_ok() accepts a free page of any > migratetype. Under ALLOC_NOFRAGMENT, a request below pageblock_order can > only take a page of its own migratetype or claim a whole free block, so > the check can pass when the allocation cannot succeed. > > Only a check whether one allocation can be served now should count just > the pages it can take. Please try actually reading this sentence, does it make any sense? It instantly reminded me of the meme classic: "Has anyone really been far even as decided to use even go want to do look more like?" > A check whether a zone has enough free memory > serves no single allocation and counts every migratetype: reclaim and > compaction free whole pageblocks across migratetypes. Oh yeah always this damned style again. What did they train the models on? > Add __zone_watermark_ok_mt(), which takes the migratetype, for the first > kind: > > - the allocator fast path, zone_watermark_fast(); > - its recheck after node reclaim in get_page_from_freelist(); > - compaction's up-front check, compaction_suit_allocation_order(). > > __zone_watermark_ok() wraps it for the second kind. kcompactd shares > compaction_suit_allocation_order() with direct compaction and passes > MIGRATE_MOVABLE, which is not read without ALLOC_NOFRAGMENT. > > Declare both in mm/internal.h: nothing outside mm uses them. > > Nothing reads the migratetype yet: no functional change. Preparation for > making the high-order check honour ALLOC_NOFRAGMENT. > > Looks good? Not really :(