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 1549D3C584E for ; Tue, 23 Jun 2026 08:54:16 +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=1782204857; cv=none; b=r1iD3exChvwFwUcvv9Uxbv21JLKctGDxNdfVVGAqKkyvqsVcWDMsq32xePKd+BdS8fqGiKUas4zlrcqUijkvnYKRzbMAjGRsXernqy3ztyi/YjHwAYmq69mtlJcBEaTVQ3a/U50vc1hSLwA63Lp39IYh2ZIY/EGJ4KC2pP1Ulaw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782204857; c=relaxed/simple; bh=NkkzlwdLBeNpRSyNvxHtwuRBbfrznb6vhf1q1EH137o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=s9K0oseppypZiO49CMC7x4zdzlCz/lf7INZOjTUPH4IajdZFCTURH0OUPnVAln4DgZoiHi/l5zmy7A2Wey1IBJDGwB/UGykWjKuLnVt52//RADHycz9gGLMibyW7RPkOIObZ46XUgguxn0qxStISp+wH/grtD/KyNl+zBSr+p9M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UUuEh2rX; 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="UUuEh2rX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 95FC71F000E9; Tue, 23 Jun 2026 08:54:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782204855; bh=esbnX1lB5kt+A69raC0Yi7SAc8yUIkuorJ+xoJqE3yk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=UUuEh2rX+g76pPzwPkpOfDilXiG+FFZE+qZXWzOJd+wXpCpKvPqma9VusGwYEYaSm 7TlUe9xuJKF8bT4h7kPfqw+g5nbbrz/L5NkicP3jK8ZbtCsFGOVpE4nrlRytqXpcaf O0CT+wKbnCE7XFvZtsLsVYV4S19nXl/acxhsZT5SVv3jAYvMzCsFbD53p4ccK4suGN Q8oN0iA5dpN0bKpmlZa/ca0+F9ixUonrR7Ul17p0li9hkhd1d8FQvxghAK1YiagWqD p+qFOBJPaPvovPQbsgyr/npotqydBBrOjIsyX32Xg13rBL6itpfN9IUiXdK5MiXg1i SfIPjBqaeILGA== Message-ID: <4358ba84-7ed0-48c0-80e4-23a00355315f@kernel.org> Date: Tue, 23 Jun 2026 10:54:10 +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 v3] mm/page_alloc: use existing highatomic reserves on the buddy fastpath Content-Language: en-US To: JP Kobryn , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, fvdl@google.com, linux-mm@kvack.org Cc: shakeel.butt@linux.dev, usama.arif@linux.dev, linux-kernel@vger.kernel.org References: <20260623004600.113347-1-jp.kobryn@linux.dev> 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: <20260623004600.113347-1-jp.kobryn@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/23/26 02:46, JP Kobryn wrote: > ALLOC_HIGHATOMIC currently provides both access to MIGRATE_HIGHATOMIC free > pages and permission to create new highatomic pageblock reserves. This > makes it unsuitable for the fastpath. > > However, the fastpath can reach rmqueue_buddy() while MIGRATE_HIGHATOMIC > reserves have free pages available. In this situation, the allocation can > fall back to other migratetypes without trying those reserves first. > > Allow high-priority non-blocking allocations to use existing > MIGRATE_HIGHATOMIC reserves on the buddy fastpath without growing them. > First tighten the criteria for reserving pageblocks so that growth may only > occur in the slowpath. Then allow fastpath usage by enabling > ALLOC_HIGHATOMIC when the GFP mask describes a non-blocking high-priority > allocation. This logic has been factored out from gfp_to_alloc_flags() to a > new function gfp_to_alloc_flags_nonblocking(). > > A UDP receive workload was run with free MIGRATE_HIGHATOMIC pageblocks > available in the target zone. Before this patch, the workload did not > consume these blocks. With this patch, eligible order-1 allocations > reaching the buddy path consumed existing MIGRATE_HIGHATOMIC pageblocks, > with no highatomic misses observed. The workload did not grow highatomic > reserves and NAPI page-frag allocations remained healthy with no failures > or order-0 fallbacks. > > Signed-off-by: JP Kobryn Reviewed-by: Vlastimil Babka (SUSE) > --- > v3: > - remove ALLOC_HIGHATOMIC_RESERVE and let ALLOC_HIGHATOMIC keep original behavior > - use ALLOC_WMARK_MIN to identify slowpath before growing reserve > - factor out non-blocking logic from gfp_to_alloc_flags() into *_nonblocking() helper > - dropped reviewed-by tag > > v2: https://lore.kernel.org/linux-mm/20260617234958.150339-1-jp.kobryn@linux.dev/ > - decouple use semantics from ALLOC_HIGHATOMIC_RESERVE > - update changelog to reflect above change and reword test paragraph > - adjust comment in PCP path > > v1: https://lore.kernel.org/linux-mm/20260616191420.52556-1-jp.kobryn@linux.dev/ > > mm/page_alloc.c | 44 ++++++++++++++++++++++++++++++-------------- > 1 file changed, 30 insertions(+), 14 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index f7db8f049bd2..7330f22e3f8f 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3247,10 +3247,11 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone, > } while (check_new_pages(page, order)); > > /* > - * If this is a high-order atomic allocation then check > - * if the pageblock should be reserved for the future > + * Slowpath (precarious) high-atomic allocations may reserve > + * a pageblock for future use. > */ > - if (unlikely(alloc_flags & ALLOC_HIGHATOMIC)) > + if (unlikely((alloc_flags & ALLOC_HIGHATOMIC) && > + ((alloc_flags & ALLOC_WMARK_MASK) == ALLOC_WMARK_MIN))) > reserve_highatomic_pageblock(page, order, zone); > > __count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order); > @@ -4473,6 +4474,29 @@ static void wake_all_kswapds(unsigned int order, gfp_t gfp_mask, > } > } > > +static inline unsigned int > +gfp_to_alloc_flags_nonblocking(gfp_t gfp_mask, unsigned int order) > +{ > + unsigned int alloc_flags = 0; > + > + if (gfp_mask & __GFP_DIRECT_RECLAIM) > + return 0; > + > + /* > + * Not worth trying to allocate harder for __GFP_NOMEMALLOC even > + * if it can't schedule. > + */ > + if (gfp_mask & __GFP_NOMEMALLOC) > + return 0; > + > + alloc_flags |= ALLOC_NON_BLOCK; > + > + if (order > 0 && (gfp_mask & __GFP_HIGH)) > + alloc_flags |= ALLOC_HIGHATOMIC; > + > + return alloc_flags; > +} > + > static inline unsigned int > gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order) > { > @@ -4495,18 +4519,9 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order) > alloc_flags |= (__force int) > (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)); > > - if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) { > - /* > - * Not worth trying to allocate harder for __GFP_NOMEMALLOC even > - * if it can't schedule. > - */ > - if (!(gfp_mask & __GFP_NOMEMALLOC)) { > - alloc_flags |= ALLOC_NON_BLOCK; > - > - if (order > 0 && (alloc_flags & ALLOC_MIN_RESERVE)) > - alloc_flags |= ALLOC_HIGHATOMIC; > - } > + alloc_flags |= gfp_to_alloc_flags_nonblocking(gfp_mask, order); > > + if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) { > /* > * Ignore cpuset mems for non-blocking __GFP_HIGH (probably > * GFP_ATOMIC) rather than fail, see the comment for > @@ -5299,6 +5314,7 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order, > * memory until all local zones are considered. > */ > alloc_flags |= alloc_flags_nofragment(zonelist_zone(ac.preferred_zoneref), gfp); > + alloc_flags |= gfp_to_alloc_flags_nonblocking(gfp, order) & ALLOC_HIGHATOMIC; > > /* First allocation attempt */ > page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac);