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=1793281031; b=xC6ltpA+Pqib0/ZVJBMIm9OiyACbhVqsc2+wZB/8us2D0kX9RMKJlbp8WAcZCijOX5IJ 8GQP0Co3ZfVDMblX2SpqM9fhu9blxS9kGfMdEz2uvPTQdhh/adAhx7WoJsWTYiWsOOpH6 AXSVCk9X1RqzCwAw4quywxNq/Y0woehEYERv6if7K2ie5M87gw5DxPA2bJs+DhY9MZu5i VtW49UKY5MCsdHoGyKnJZXCO8xGZcXqAqSCmfgGRDE2It0j9KOl36EmCXh1WQiwB5fu1N E/PWPJ9bHVt+u1mnd6DZ5b7Mmrg/gvk1lQ9LaWRPWePQJoswkfLuw+UJT3cGNUzABhQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793281031; 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=yusQ/gNp1al5ffFyiPFxovqkMkBkDvq1/V1A+G8KNP8=; b=tLdJAOrx50SwXPyaXfUlimDvpD/uxyU5zCFBt/onJNmK+Lhkl4cMSAAJWGokDMmARxm4 Fem5dE+im9awOvat4s1ooi4ay2eZmWhwxYY/fibccaiqpC0g1Hz0pguosmixT2ccl6xzG SAfdCmRiyQdRCVBAagN3XnbIa5P8PPCkDHg+97sittPV8E3JAz8LodGMG5kuNmWendDNm Nh0zVi7OogDmfK+8M77OwFcdzhLHsj+jGWiy0utAqXLkryjxXNmXnkndv4QMSIGQk334M dOwk+iRyNcbMEdFAWjwR+IZTzKbOfSjBgIK0CZzevk7LkGqoHzOOp5AbAZHlFWDmKdg== 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=fIXuH3oP; 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 CE24960A382A; Thu, 29 Oct 2026 13:37:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=fIXuH3oP Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2692A1F031EC; Thu, 29 Oct 2026 13:37:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793281030; bh=yusQ/gNp1al5ffFyiPFxovqkMkBkDvq1/V1A+G8KNP8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fIXuH3oPbKOQqHa+sb82A1lqdGEE0KcOgjF+PatDaFm43q0tXh6aZfgHVTPVkzhK8 jR0yOowvlHMK1RAA3Gh8EHvmNFZ190IgWKCan6bh89OQ1KHejC1cxKJrwPjErgz80o GtZ2nO9DmLB3ry90DZ0LhmjrKBrm9bdOrPRHbKa5tH3YviCk87S5bMVhZiS13bbaTE diYUiyFFeavhUjIW73ix4dDOFSqJsVIrEM0rBfDWS9QMA8oCUgO6HMKrQk71Ol0HKC t7wrO2vnOAMFY65gPgYkcD9GNDNEe1748kh2kCS7PeaNEk3VFGgZjLQKCOwc3IihDq 15/bp4/cVuzDg== Message-ID: <68fd8182-cdfb-4f11-95de-1472e6c92d33@kernel.org> Date: Thu, 29 Oct 2026 14:37:03 +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 v4 1/8] mm/page_alloc: reset can_retry_reserves when the slowpath restarts Content-Language: en-US To: "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, mgorman@techsingularity.net, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20261028211930.3504634-1-gourry@gourry.net> <20261028211930.3504634-2-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: <20261028211930.3504634-2-gourry@gourry.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/28/26 22:19, Gregory Price (Meta) wrote: > Commit 2c4c3e29897d ("mm/page_alloc: simplify __alloc_pages_slowpath() > flow") retries an allocation once with reserve_flags when the caller > becomes eligible for reserves, guarded by can_retry_reserves. The flag > is set at its declaration and never reset. > > A restart after a cpuset update or a zonelist rebuild drops > reserve_flags I don't follow, nothing "drops reserve_flags"? after the restart, there will still be a get_page_from_freelist() without them followed by get_page_from_freelist() with them, right? > and comes back with can_retry_reserves already false, so a > caller that cannot reclaim, such as GFP_NOWAIT | __GFP_MEMALLOC, fails > without trying the reserves again. The "goto retry" triggered by can_retry_reserves actually drops nodemask and recalculates preferred zones. Perhaps "can_retry_reserves" wasn't the best name. > Reset can_retry_reserves at restart. Only a cpuset or zonelist change > restarts the slowpath, so the retry still runs at most once per change. > > With kprobes failing every attempt without reserves and the first with > them, and a memory block onlined during the walk, the allocation > returned NULL in 3 of 3 runs, and a page in 3 of 3 with this change. So IIUC the allocation was racing with a memory online in a way that it would fail if the online happened fully after the allocation. So this just turns part of the race window into the allocation's favor? > Fixes: 2c4c3e29897d ("mm/page_alloc: simplify __alloc_pages_slowpath() flow") > Cc: stable@vger.kernel.org > Signed-off-by: Gregory Price (Meta) I mean it's not wrong and if patch 5 depends on it (unless it also only fixes a racy window in the same way I think is happening here) then so be it. But the commit log would need correcting. > --- > mm/page_alloc.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 2daf358269ae..78569ac6f2d9 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4783,7 +4783,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > unsigned int zonelist_iter_cookie; > int reserve_flags; > bool compact_first = false; > - bool can_retry_reserves = true; > + bool can_retry_reserves; > unsigned long alloc_start_time = jiffies; > > /* > @@ -4817,6 +4817,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > no_progress_loops = 0; > compact_result = COMPACT_SKIPPED; > compact_priority = DEF_COMPACT_PRIORITY; > + can_retry_reserves = true; > cpuset_mems_cookie = read_mems_allowed_begin(); > zonelist_iter_cookie = zonelist_iter_begin(); >