From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794561479; b=qBf0GB9TsiBt9iDP7yHUCBSSYHJZ6G58LHs7Tgrn9ulHDA49GoZGH4+NvXwN7V+YAK9w KMwdkeudWxbVmuTWEBorwEf451Eblz2SGlGWupNpFVYnCsof8Tk6UCEHP/JvDJwslnGBz joWL+q1+rzLDZHoAaDTVFR4JKZ2a7fPsJ1utzQ3jZ0fgtBU19X3NOo9r5TPZ4SU75vvuJ sg8XFzzK9WLt1oOHG7uRpc31pCdRIvxJP9khtvqmoCk5Yc0LuiW3ZSGQFyftH7tv6m7vq U3D/zyAdYrY2n5SLm5D/imJGeDD1dfQYeKnygHKPx5lGb3MzIKZuS6Xzs0i8YIxd8tQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794561479; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:Content-Language:To:Cc:References:From:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=eStupLSXeWq6p5mACFQucqZl8B+vHFCM7s/qEMYl1DA=; b=mb+L4IwDEsjiSBAeXANweVb0JeYV+rzTkKGfDbS7HsCZAQf13Q03C27oDiPPBwfL0oHo tjDD1jyVFn7GoOUga1uxlJZN+cH1MVHctwwDGFD414bBnN8fXrQYIiTIXHFCcTyL8OIG/ W+R9LljIRpufDXKh0JtiSrkc7CPtv5MIGm6Y0g7uaPenteYrJpUCYYLxEMnK0T01i/Atv +LRIQLC12Ng4bNA29g8760I5ql45TKCg54togstQuNf3/owbhnE+hV9/VvQvaL8LUKOf9 cjb/v9QHu0b8NXFTIpdav2utDvTxw7gon5JKqgKXMMlTZb7jv60FOvxhY3pJnPOnzkg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=lp8IreAf; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A6E73606A31C for ; Fri, 13 Nov 2026 09:17:59 +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=lp8IreAf Received: by smtp.kernel.org (Postfix) with ESMTPSA id B7FA51F000C4; Fri, 13 Nov 2026 09:17:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794561479; bh=eStupLSXeWq6p5mACFQucqZl8B+vHFCM7s/qEMYl1DA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=lp8IreAfVoWjkixVIy9DCUXHkhoExRX0F1bbq7RlUuuTLL2eI+T7WMiDI5rw6sIv+ Tm2Suo/+oDXFjmRwIiOnV02E4vaOWMUZ8wTK/EJAeUrdGwkD26bi30Vw8xnP/kIV98 u7ddgT8/w0FqgbOAedwo4GGOSF4BjyPO/jdwIfbdfuaYHbCW2mLAR0Bv8XNN52x2dt RxgOs0ydh/zyJPL/0Pug88P7wSdbgFS3HkokHC8vobelXDq1P+NMXkg+e3grB/8qcc jEcjzrWoR30bVGhisVhMc6gHD9Yr99w1Sdg6Ylsj6TL0yP959LlIrHJl2PfcF12YSh RgyN/1I/zeC4g== Message-ID: Date: Fri, 13 Nov 2026 10:17:54 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_alloc: only skip kswapd nodes below their kswapd watermark Content-Language: en-US To: Joshua Hahn , Johannes Weiner , Gregory Price , "Lorenzo Stoakes (ARM)" Cc: Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Zi Yan , "Jose A . Perez de Azpillaga" , Daniel Hodges , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20261112214738.3002458-1-joshua.hahnjy@gmail.com> 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: <20261112214738.3002458-1-joshua.hahnjy@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/12/26 22:47, Joshua Hahn wrote: > Commit 19c5fb83f2a4 ("mm: page_alloc: avoid kswapd thrashing due to > NUMA restrictions") makes get_page_from_freelist() skip any node with > kswapd running to avoid piling on already-pressured nodes. > > This assumes that kswapd was woken to create free space, although kswapd > can be woken up for other reasons, like higher order allocation > failures. Thus, fragmented nodes with failed high order allocations will > always wake up kswapd and direct order-0 allocations to the fallback > path, even when there is free space. > > This behavior was observed on 2-NUMA Meta production workloads where > faults would pile on already pressured remote nodes while stranding > memory on the relatively empty local node, causing unnecessary pressure. > > Only skip nodes with kswapd running if the node is under the relevant > low-memory watermark. > > On a 2-NUMA VM with a 60G node0 and a 20G node1, with THP enabled=always > and defrag=defer, I ran a process that prefers allocating on node0. > With a fragmented node0: > - Before the patch, 66% of faults were served from node0 > - After the patch, 100% of faults were served from node0 > > Fixes: 19c5fb83f2a4 ("mm: page_alloc: avoid kswapd thrashing due to NUMA restrictions") > Suggested-by: Daniel Hodges > Reviewed-by: Jose A. Perez de Azpillaga > Reviewed-by: Johannes Weiner > Reviewed-by: Lorenzo Stoakes (ARM) > Acked-by: Gregory Price (Meta) > Acked-by: Zi Yan > Signed-off-by: Joshua Hahn > --- > v2 --> v3: > - Shortening cover letter, suggested by Gregory and Johannes > - Collect signatures > > v1 --> v2: > - Added a Fixes tag and separated this from the other cleanup patches > - Check zone_watermark_fast with no flag to match the call in > pgdat_balanced(). > - Calculates mark outside the zone_watermark_fast check to match the > style for the other zone checks. > - Wordsmithing commit message to explain the unaddressed gap. > - Yes, this is ugly. I have another series to clean this code up but > I wanted this to be a feature-minimal patch so that it could be > easily backported. Things will be much prettier once those are landed. Easily backported, but there's no Cc stable. So I'm adding it as it seems useful enough for LTS kernels. But at the same time not urgent for rcX hotfix. Applied to page_alloc/for-next, thanks. > > mm/page_alloc.c | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 8532af052d74b..56121c3f9c4a7 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -45,6 +45,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -3799,6 +3800,9 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags, > struct zoneref *z; > struct zone *zone; > struct pglist_data *last_pgdat = NULL; > + enum zone_watermarks kswapd_watermark = > + sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING ? > + WMARK_PROMO : WMARK_HIGH; > bool last_pgdat_dirty_ok = false; > bool no_fallback; > bool skip_kswapd_nodes = nr_online_nodes > 1; > @@ -3866,16 +3870,21 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags, > } > > /* > - * If kswapd is already active on a node, keep looking > - * for other nodes that might be idle. This can happen > - * if another process has NUMA bindings and is causing > - * kswapd wakeups on only some nodes. Avoid accidental > - * "node_reclaim_mode"-like behavior in this case. > + * If kswapd is already active on a node and the zone is below > + * its kswapd watermark for this request, keep looking for > + * other nodes that might be idle. This can happen if another > + * process has NUMA bindings and is causing kswapd wakeups on > + * only some nodes. Avoid accidental "node_reclaim_mode"-like > + * behavior in this case. > */ > if (skip_kswapd_nodes && > !waitqueue_active(&zone->zone_pgdat->kswapd_wait)) { > - skipped_kswapd_nodes = true; > - continue; > + mark = wmark_pages(zone, kswapd_watermark); > + if (!zone_watermark_fast(zone, order, mark, > + ac->highest_zoneidx, 0, gfp_mask)) { > + skipped_kswapd_nodes = true; > + continue; > + } > } > > cond_accept_memory(zone, order, alloc_flags);