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=1793267400; b=QRkImSWF40rvQ4hdKXOCkO4/IV6Q0L9IaIu9jX0nc08eRsCgH0/MleLwFDZC08Om06To ox4mVGiWgeaKhSF3Qs2gk7xyYs4BJ6LQ/31g2GPMof/VXVeTcJaU66ekEESvL3qAT4P3D MaATI6Bkyzo5jKzB4hD3sdCO0CxAs1Hw3N/P0h2NnQPwaSdESUlPRkB5YoIT1bh/fANz3 EF3sM8R7JjTv3NGgcAdy2YFqAbPo40hLJqevlBr34AODLHUhoGjBP/iQ3j7aKmiON4oc7 8pC52agP8RlZhUyNs7f6yJy8q8Qgche3oO/JqDxfNNJI78aUkSZJmGu7YMjuCD3+Ufg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793267400; 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=Ia0Mtm3zy/9bRYGZBaX24d9DjUyjcJwGOTQAf9z14P8=; b=Dj8zMl6X6CTg7NuCXQtFEt+dUqCInx8CkxFUAkr0DW9RIrfcpZm/bVH1yMPnYvELzLyk wa07y5shlvZwnCFWFJldHvivZGxhj4Gy4SD+nPqmhcrKwXkWnVEX+bEUfMdRGcEoaZd7+ qE0QY6gutu4owUyldVDDzOTUPzfRQOkqeHl/ssAPUHpnxEgEA/c96yafbiWB37RQK4l3f P8tki2x95ZNKiTJzFZPqWbR3kx5u/tLXPH3AgBveVGb48h7iSoQTCLZle6Z8tIsB3rl2X tfTqK6DNfWd4LyZF9F0aUjU8ry2NvdzkoE9tdtcH7aR0TT366BkdcaFRyb3b/JE435Q== 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=l6l6g97f; 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 640BC606A31F; Thu, 29 Oct 2026 09:50:00 +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=l6l6g97f Received: by smtp.kernel.org (Postfix) with ESMTPSA id F36DA1F031E1; Thu, 29 Oct 2026 09:49:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793267400; bh=Ia0Mtm3zy/9bRYGZBaX24d9DjUyjcJwGOTQAf9z14P8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=l6l6g97ftKGETwe9W+MgWjB7StxSM/rVyuw87s1BGU7VPUbP4jpcnKr+cLkBw1ym4 2fFxA8DyzSMtnmtuppQVDmKr2v60BVjWnZ9wwNmhttPQfkgNceKO6BjypqhXsEkHwe x5s/RRZgYbPhDo/ygFvmqmqWAP7Lmv1wVCBrtn4LDqBFKPRsGdZFBM5rB1Q1ztxo9f LSUvmic9nHXt8/ZyZG4fdyAy1iqul0fJd4do3I3sPN0C92jftCAGhHw0gXpglGLLJF 7f6jS0ePCDTOhaVGFBvmoBRhtmZHHfoNPyo//JqpZCvvSutgP5vz5wYWa2JKdIf+NB YMfPInhXkqAEA== Message-ID: <3126db67-8ac8-4913-bd4a-4008de730148@kernel.org> Date: Thu, 29 Oct 2026 10:49:54 +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 1/2] mm: page_alloc: do not give all non-blocking requests reserve access Content-Language: en-US To: Johannes Weiner , Andrew Morton Cc: Matthew Wilcox , Salvatore Dipietro , Christoph Hellwig , Dave Chinner , Matt Fleming , Mel Gorman , Michal Hocko , Suren Baghdasaryan , Brendan Jackman , Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko , stable@vger.kernel.org References: <20261028171719.2043421-1-hannes@cmpxchg.org> <20261028171719.2043421-2-hannes@cmpxchg.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: <20261028171719.2043421-2-hannes@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/28/26 18:15, Johannes Weiner wrote: > 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access > highatomic reserves") accidentally gave all non-blocking allocation > requests access to highatomic reserves, which includes GFP_NOWAIT and > other sites clearing __GFP_DIRECT_RECLAIM. > > While this improved atomic request success rate, it's unintentionally > broad and can actually worsen highatomic requests by squandering the > reserves on requests that don't need it. > > There are concurrent efforts to clear __GFP_DIRECT_RECLAIM altogether > for costly order __GFP_NORETRY requests, which would then also fall > into this exemption and deplete reserves even faster. > > What GFP_ATOMIC has over the others is __GFP_HIGH, which > alloc_flags_slowpath() translates to ALLOC_MIN_RESERVE. > > Narrow the exemption to contexts that have both ALLOC_NON_BLOCK | > ALLOC_MIN_RESERVE. > > Reported-by: Sashiko > Link: https://sashiko.dev/#/patchset/20260904115629.3993331-1-dipiets@amazon.it > Fixes: 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves") > Cc: stable@vger.kernel.org > Signed-off-by: Johannes Weiner Reviewed-by: Vlastimil Babka (SUSE) > --- > mm/page_alloc.c | 4 +++- > mm/page_alloc.h | 3 +++ > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a8cac5e01066..8ac2e2bf14fc 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3238,7 +3238,9 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone, > * reserves as failing now is worse than failing a > * high-order atomic allocation in the future. > */ > - if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK))) > + if (!page && > + ((alloc_flags & ALLOC_OOM) || > + (alloc_flags & ALLOC_MASK_ATOMIC) == ALLOC_MASK_ATOMIC)) > page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC); > > if (!page) { > diff --git a/mm/page_alloc.h b/mm/page_alloc.h > index e238ee91ed24..9c3c2830acb0 100644 > --- a/mm/page_alloc.h > +++ b/mm/page_alloc.h > @@ -60,6 +60,9 @@ > /* Flags that allow allocations below the min watermark. */ > #define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM) > > +/* Flags that mean GFP_ATOMIC */ > +#define ALLOC_MASK_ATOMIC (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE) > + > /* > * Structure for holding the mostly immutable allocation parameters passed > * between functions involved in allocations, including the alloc_pages*