From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 7D8916079D49 for ; Fri, 13 Nov 2026 17:48:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=je/EUNBi Received: by kanga.kvack.org (Postfix) id 7BFFF6B05C1; Fri, 13 Nov 2026 12:48:48 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 797BD6B05CF; Fri, 13 Nov 2026 12:48:48 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 685EF6B05D1; Fri, 13 Nov 2026 12:48:48 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 3FA256B05C1 for ; Fri, 13 Nov 2026 12:48:48 -0500 (EST) Received: from smtpin26.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id CB76DA797C for ; Fri, 13 Nov 2026 17:48:47 +0000 (UTC) X-FDA: 85430831094.26.BC229D0 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf11.hostedemail.com (Postfix) with ESMTP id E9D4D40005 for ; Fri, 13 Nov 2026 17:48:45 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="je/EUNBi"; spf=pass (imf11.hostedemail.com: domain of vbabka@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1794592126; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=8QE0lBItlXqLLZsb6/W5u8fuKfBnTPnnw9b1Lz54dEM=; b=NjrGx/RhabI2t9XOTeK00iN4lm50/HrtFyeBSTRz2IXgo3tGennwHdt6aaxOkPAslVaEl6 IKL6Mgfe8/kcH2T4Lv6wpmFifif6BRKsRqbigFxghOeZU8SRJlvVLh0ZIfCvyO7jOZFqFw dl4EBMEXsFkPWxuRe/P1WvKzb+aU7b4= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1794592126; b=4Ucx4rBUa2lLpzD5jp3HRDe9Bb4JUt698vRhZWCW+9SWpPVg6S6tV9e9XT9erv2UOMm3Pt cue9IaYD4ZCP0GNy6MaX7q9RjcwnF9J5Nf/KljZXDguk/5mcEKRq8XR0hVJfyhQomeVKTT ky1BECnHmDSFVVffsUV07u9JVArLZco= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="je/EUNBi"; spf=pass (imf11.hostedemail.com: domain of vbabka@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 2A79140E93; Fri, 13 Nov 2026 17:48:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E9E1D1F000C5; Fri, 13 Nov 2026 17:48:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794592125; bh=8QE0lBItlXqLLZsb6/W5u8fuKfBnTPnnw9b1Lz54dEM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=je/EUNBicrrps5U0MfpbWr7DpEg6xZPbOw8lC68mHafP/SxKyGoY70T9fgJQIwY/w UsutT+SXhSIQeK3Tne6UI95e3XwuHnSq0opGdidq/hptHe5PPDW+3eCqAsa/i2Olgj YOCRNfJA0IKDYK48PwHJP3CQMu7fehzOIeHTlBZBw7h5CNDsiBJfZiPQ2ELCyYFz6A Ypuxsqq1M0QK/LQ81bT8E9YuRliroWUEZ/XWrkR/eJzhcA3JTpLR5WHqB3aQVOSa+U lVcTapZDsm3UWeeAuoRw39vC6qzd7spQ9tfrLlaId2xGE5WQBpdEEH3YqQYgFUeTBN e0O/9nt0gLR0g== Message-ID: Date: Fri, 13 Nov 2026 18:48:37 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm: page_alloc: make the high-order watermark check honour ALLOC_NOFRAGMENT Content-Language: en-US To: "Kiryl Shutsemau (Meta)" , Andrew Morton , Johannes Weiner , David Hildenbrand Cc: Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Zi Yan , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Qi Zheng , Shakeel Butt , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , Dev Jain , Harry Yoo , Usama Arif , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20261102093939.3340540-1-kas@kernel.org> <20261102093939.3340540-3-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: <20261102093939.3340540-3-kas@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Stat-Signature: hu5qk78ra7kzxk37q115fm1nggzh6b1t X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: E9D4D40005 X-Rspam-User: X-HE-Tag: 1794592125-456159 X-HE-Meta: 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 tZEzZdsu 927H68qaFqN1GcE7OEkWrRLP7eoLCSV2VrjYFD3/PIweTYdiTO22w3SydVZFSs5hH6r96QDBLxojw47TPF15SinQ36ul556wRTR7hZZb+UoV1X9+kn2cX1TTJGLdwFLU0sUsGtd7yK3IGdNoJzfvmAu5AsmJQsItDsqlr6ryiXFBFwN1Aw1AUNYj+i0RiBJc0+uoEZ/H8Tk0KyU1mPJFQVK36Cz/HX0x/g7ENn2vaVeY+OgfL10R1U4pkOgYGcy+KPvsmUGHE4ysBHSH0X/X25diDDMqE1EpgWJtnSPnYcmr1M8j7jz++MAJG26Nbf3Qzqs8aPkm7YkeAtSzxHbpsVAdkc4VdQQ/TFmhaC3pTsJy92JxyTfGpDiByl4c7uwZHtywQDJLj6VnmoyI= 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 11/2/26 10:39, Kiryl Shutsemau (Meta) wrote: > With defrag_mode, every slowpath allocation carries ALLOC_NOFRAGMENT. A > request below pageblock_order may take a page of its own migratetype or > claim a whole free block, but not steal from another migratetype's block. > The high-order part of the watermark check still accepts a free page of > any migratetype. > > Under memory pressure, movable allocations take free movable pages as > soon as reclaim frees them. Free space in unmovable and reclaimable > pageblocks is off-limits to them under ALLOC_NOFRAGMENT, and builds up. > The free pages of order 4 and up end up mostly in those pageblocks. > > A 64K mTHP fault cannot take them, but direct compaction's up-front check > counts them and returns COMPACT_SUCCESS without compacting anything. The > allocation then fails. Because compaction "succeeded", it is never > deferred, and every fault stalls in it again before falling back to small > pages. > > Dev Jain's benchmark faults 64K mTHPs under swap pressure, in a 7G VM > with only the 64K size enabled. With defrag_mode, those faults stall in > compaction 18 times as often and get about a third of the folios > (medians of 15 runs): > > defrag_mode=0 defrag_mode=1 defrag_mode=1 > + this patch > compact_stall 1690 30669 2607 > compact_fail 621 30531 906 > 64K faults allocated 20750 7391 11538 > 64K faults falling back to 4K 725 13832 9945 > > Make __zone_watermark_ok_mt() skip other migratetypes' free lists below > pageblock_order for an ALLOC_NOFRAGMENT request. Give > __compact_finished() the same rule for its fallback test, so that > compaction, once it runs, stops on a page the request can take. > > zone_watermark_fast() calls __zone_watermark_ok_mt() too. With > defrag_mode, an allocation now wakes kswapd and starts reclaim or > compaction as soon as the free lists hold nothing it can take. For the > orders the per-cpu lists serve, that is earlier than before: the check > does not count their pages, so the allocation no longer uses up the local > list first. A request that may not wake kswapd or reclaim, such as an > mTHP fault with THP defrag=never, falls back to a smaller folio instead. > > Fixes: e3aa7df331bc ("mm: page_alloc: defrag_mode") > Reported-by: Dev Jain > Closes: https://lore.kernel.org/all/4aa14b41-9b89-494c-8825-55fffd5a541c@arm.com/ > Tested-by: Dev Jain > Signed-off-by: Kiryl Shutsemau (Meta) This seems fine enough. > --- > mm/compaction.c | 5 +++++ > mm/page_alloc.c | 21 ++++++++++++++++++--- > 2 files changed, 23 insertions(+), 3 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 6c553d0e90f8..7b2267bbf115 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -2365,6 +2365,11 @@ static enum compact_result __compact_finished(struct compact_control *cc) > !free_area_empty(area, MIGRATE_CMA)) > return COMPACT_SUCCESS; > #endif > + /* Under ALLOC_NOFRAGMENT it may only claim a whole block */ > + if ((cc->alloc_flags & ALLOC_NOFRAGMENT) && > + order < pageblock_order) > + continue; > + > /* > * Job done if allocation would steal freepages from > * other migratetype buddy lists. > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 7730660bdd09..d53fb2c67ae1 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3586,6 +3586,11 @@ static inline long __zone_watermark_unusable_free(struct zone *z, > * will return true of the order-0 watermark is reached and there is at least > * one free page of a suitable size. Checking now avoids taking the zone lock > * to check in the allocation paths if no pages are free. > + * > + * Under ALLOC_NOFRAGMENT, a request below pageblock_order can take another > + * migratetype's page only by claiming the whole block, so only free pages of > + * @migratetype count below pageblock_order. Without ALLOC_NOFRAGMENT, > + * @migratetype is not used. > */ > bool __zone_watermark_ok_mt(struct zone *z, unsigned int order, > unsigned long mark, int highest_zoneidx, > @@ -3648,6 +3653,9 @@ bool __zone_watermark_ok_mt(struct zone *z, unsigned int order, > continue; > > for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) { > + if ((alloc_flags & ALLOC_NOFRAGMENT) && > + mt != migratetype && o < pageblock_order) > + continue; > if (!free_area_empty(area, mt)) > return true; > } > @@ -3677,8 +3685,12 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, > int highest_zoneidx, unsigned int alloc_flags, > long free_pages) > { > + /* Serving an ALLOC_NOFRAGMENT request needs __zone_watermark_ok_mt() */ > + VM_WARN_ON_ONCE(order && order < pageblock_order && > + (alloc_flags & ALLOC_NOFRAGMENT)); > return __zone_watermark_ok_mt(z, order, mark, highest_zoneidx, > - alloc_flags, free_pages, MIGRATE_MOVABLE); > + alloc_flags & ~ALLOC_NOFRAGMENT, > + free_pages, MIGRATE_MOVABLE); > } > > bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, > @@ -4685,10 +4697,13 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order, > > /* > * Would the allocation succeed if we reclaimed all > - * reclaimable pages? > + * reclaimable pages? Count free pages of every migratetype: > + * reclaim and compaction work across migratetypes to free a > + * whole pageblock, which the allocation can then claim. > */ > wmark = __zone_watermark_ok(zone, order, min_wmark, > - ac->highest_zoneidx, alloc_flags, available); > + ac->highest_zoneidx, > + alloc_flags & ~ALLOC_NOFRAGMENT, available); > trace_reclaim_retry_zone(z, order, reclaimable, > available, min_wmark, *no_progress_loops, wmark); > if (wmark) {