From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E1CE94A6CFA; Thu, 15 Oct 2026 07:51:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792050715; cv=none; b=RlcUu5vIXs7mtDp91cnIFanRS2zZ94AbZh1KkhUhALrHKwPuA4k0GjxnqxTa5S64PdyiAILmoIQkRk+FPtMNOkrScmUmlxCh02m+XUSAQVU6cO1uaxyitCJhj1TCdWb6+U5wOG2Foukn2IYN+PKLm677rSugKUfd6Ye5RFw5PFY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792050715; c=relaxed/simple; bh=58MGJzsg/gzKE9+ctrzXojPWzyH5En6609u7hKIGXXY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NHQvhgXlE07nJrODHXw8WN+Jqw2uJkYwpCBtFs7svsIii2flbxdj9PXCsMPbpSd43O5vpavaz7dp/d3l5mO3Yjpo2+QUoWIzlt5r8lZRvQhLQpZgE/5NSD+zZC3GoSMpILU1H9aNEpGVRClNPodNiE1+pu/I6575eGLX/3RfnUg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oBSxGh4f; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oBSxGh4f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2CA0C1F000C4; Thu, 15 Oct 2026 07:51:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792050708; bh=UJe2c3nr2fvv5KSBUYY6ev4UYSzq43r8K4rqLE7u2ow=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=oBSxGh4fID9Jb/BaBMZN/U6FvOCiPd6N7cRzVv5ZUHrqBrbIrcIWGCcvXVMGTheuJ W+qG1lbxXHer5r+0wuQve1Q6pTvKVtG6Gx7k0OQek3+MdJt6uKWVtS+SPRUZ06wwGH +TlkcYsOavW/HhicDk4ctMOHY3Ed6Ss1utyQniU9T67YS9V0PHcZh92SFNKiLXLj96 VBFVPmsIHDD5WEaaFofdaYG7yqvMM/vAUD/ZszvtHeZJ1w3TCo8kNcB+9U70BJeN5B d7v2BRD4I7h5hZV5j0V650CJxbPZPe4h5Updm4umkoiRfZFMOWWfdtL5tXCl/KceGc iM+rAPtYeGrxw== Message-ID: <8b312a3c-5985-4da1-be5f-11364e662363@kernel.org> Date: Thu, 15 Oct 2026 09:51:43 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/page_alloc: detect zonelist rebuilds from memory hot-add Content-Language: en-US To: "Gregory Price (Meta)" , linux-mm@kvack.org, cgroups@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, longman@redhat.com, ridong.chen@linux.dev, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, akpm@linux-foundation.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, ziy@nvidia.com, david@kernel.org, mgorman@techsingularity.net References: <20261014222456.2318284-1-gourry@gourry.net> <20261014222456.2318284-2-gourry@gourry.net> 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: <20261014222456.2318284-2-gourry@gourry.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/15/26 00:24, Gregory Price (Meta) wrote: > The zonelist_update_seq retry was limited to CONFIG_MEMORY_HOTREMOVE, > presumably because only hot-remove takes zones out of a zonelist. > > However, build_zonerefs_node() rewrites the zonelists in place, so > onlining the first block of a zone shifts the entries that follow it > in every zonelist containing that zone. This can cause a spurious > allocation failure for a __GFP_THISNODE caller. > > For a node with only ZONE_NORMAL, onlining its first ZONE_MOVABLE block > rewrites the node's ZONELIST_NOFALLBACK list as: > > [NORMAL, NULL] -> [MOVABLE, NULL] -> [MOVABLE, NORMAL, NULL] > > A concurrent GFP_KERNEL | __GFP_THISNODE allocation can observe the > intermediate list, skip ZONE_MOVABLE, and find no eligible zone. With > CONFIG_MEMORY_HOTREMOVE=n, check_retry_zonelist() returns 0 and the > allocation fails even though the node has free ZONE_NORMAL memory. > > Gate the sequence checks on CONFIG_MEMORY_HOTPLUG, which covers every > configuration that rebuilds zonelists after boot. > > Fixes: 3d36424b3b58 ("mm/page_alloc: fix race condition between build_all_zonelists and page allocation") > Signed-off-by: Gregory Price (Meta) Reviewed-by: Vlastimil Babka (SUSE) > --- > mm/page_alloc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 7682aecc2c075..81db19f2ab551 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4425,7 +4425,7 @@ static DEFINE_SEQLOCK(zonelist_update_seq); > > static unsigned int zonelist_iter_begin(void) > { > - if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE)) > + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) > return read_seqbegin(&zonelist_update_seq); > > return 0; > @@ -4433,7 +4433,7 @@ static unsigned int zonelist_iter_begin(void) > > static unsigned int check_retry_zonelist(unsigned int seq) > { > - if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE)) > + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) > return read_seqretry(&zonelist_update_seq, seq); > > return seq;