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=1794585904; b=xBW+AqYVrl3P3eqmkq+0nhouGO8yFfwoj0yrr5jXOQWgcOGfLPnQr1XMxSIxVyQsVYwN B3JAcyr9kEKeNey+0Kp6nVEwdg61jhR9Bmqrp7HSkALqVqk0wPxf3KC/aC+ylYkCLcCTS GTF8/Eef9kPjovuGq6idJBXF9O0XHrWsBdmaivfZmQXfpHGKFjB5aF7UDo8CYpCdubI2/ 1tyo/K9RzmkNOeZliTp1Ry31KTSXF4RKPvPVWwexGjESxb/fYvZDncRKIGk5INCv7S1az imPZbJFD3+iLTwVyodWhwwLbcccS7+2BjMQVdBQ7O4viByho9IJUib/TA8RCGHdxoLA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794585904; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=03xzFy3NxNxscO2+Ya/UCSedpqUldR1nqa7/+wp4LPY=; b=jah3xukIlHUuTYJa5VHNsYjSmtcxbbwIs5xe+MxtwKdtWl1hivaDpZZiL6Re4ldoUvY1 3Mv/ajM+XLRldL+CdpmEY3UvDjUb3WfGUt3eoje4ZnBtxyrTQFDZFPQb5Ab5nKGpiZV5H 1o+bQa2mArqR3g+dy6A7DxDbjdDMMMvrkdxHMKuA5TIn1HTOD7cpeoAkhtHeIahAJF1nf iLPUvvuCiZR1qepSUKJNUPxn9gw5LFy1e5173fSv/P8fed7V4k0lNOGkDxeu9jIW37gvk Nk29M/2yUkQxM+uvTrUihpOmZraB/gc7CFxcs4fh/zDPbE1bvLlmSYcQ5IAyjQWqtXw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=nLCxrakM; 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 DA2866070943; Fri, 13 Nov 2026 16:05:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=nLCxrakM Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7A3901F0181B; Fri, 13 Nov 2026 16:05:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794585904; bh=03xzFy3NxNxscO2+Ya/UCSedpqUldR1nqa7/+wp4LPY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nLCxrakM56Y/p3WyeqYxgN5FZjO7bFh3FjIhX0sfug/hKaTKHs1MbsalF5cCFELWB hVSGh1KijithJTuQVfHBDJVrkz0BqE1XxxanbMkNnlbMrS/x1N6dSqi750V2E8jBZg As8e6GeFiNoXS/ilQahDIhI03gPqMCtGc1JVLJ3Q= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Salvatore Dipietro , Andrew Morton , "Vlastimil Babka (SUSE)" , Zi Yan , Johannes Weiner , Christoph Hellwig , David Hildenbrand , Michal Hocko , Matthew Wilcox , Dave Chinner , Ritesh Harjani , Dmitry Ilvokhin , Hazem Mohamed Abuelfotoh , Ali Saidi , Geoff Blake , Christian Brauner , dipietro.salvatore@gmail.com, "Darrick J. Wong" , Brendan Jackman , rvvandan@amazon.com, Suren Baghdasaryan , "Garg, Shivank" , Sasha Levin Subject: [PATCH 7.3 470/507] mm/page_alloc: avoid direct reclaim and compaction for costly __GFP_NORETRY allocations Date: Fri, 13 Nov 2026 10:52:54 -0500 Message-ID: <20261113153812.682020080@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153753.358973689@linuxfoundation.org> References: <20261113153753.358973689@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Salvatore Dipietro [ Upstream commit 0e05a469c29400eb6e35448ce7318581688a1806 ] Commit 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") introduced high-order folio allocations in the iomap buffered write path. When memory is fragmented, each failed costly-order allocation enters __alloc_pages_slowpath() which runs direct reclaim, direct compaction and drain_all_pages(), causing a 0.38x throughput drop on PostgreSQL pgbench (simple-update) with 1024 clients on a 96-vCPU arm64 system. The root issue is that direct reclaim and direct compaction are too expensive for hot allocation paths that have fallbacks to smaller allocations. __filemap_get_folio_mpol() already marks higher-order allocations with __GFP_NORETRY | __GFP_NOWARN, signalling that the caller can handle failure. However, the page allocator still enters the full blocking slowpath for costly orders with __GFP_NORETRY, which is unnecessarily aggressive when the caller will simply retry at a lower order. For costly-order allocations with __GFP_NORETRY, clear __GFP_DIRECT_RECLAIM at the very start of the slowpath, before can_direct_reclaim, can_compact and the nofail checks are evaluated. This makes the entire slowpath treat the request as non-blocking: no direct reclaim, no direct compaction and no drain_all_pages() IPI across every CPU. Reclaim and compaction move to the background instead: kswapd is still woken for reclaim, and it wakes kcompactd for defragmentation. The system keeps its long-term health while the latency-critical direct allocation path no longer stalls. Allocations that also request __GFP_THISNODE are exempted. That flag pairing identifies the local-node-first THP attempt issued by alloc_pages_mpol() (mempolicy.c), which relies on direct compaction to form transparent huge pages. Clearing __GFP_DIRECT_RECLAIM makes these allocations reach the !can_direct_reclaim bailout, which since commit 4c0ed883e051 ("mm/page_alloc: fix defrag_mode for non-reclaimable allocations") drops ALLOC_NOFRAGMENT and retries instead of failing when defrag_mode is on. With vm.defrag_mode=1 a __GFP_NORETRY allocation could therefore succeed by fragmenting another migratetype's pageblock. That is the wrong trade for a caller that has already communicated it can handle failure and has a cheap lower-order fallback, so exclude __GFP_NORETRY from the relaxation. The exclusion is not restricted to costly orders: any __GFP_NORETRY caller has said it can cope with failure, so failing is preferable to fragmenting for all of them. Test environment: Hardware: AWS EC2 m8g.24xlarge (96 vCPU, arm64) 12x 1TB IO2 32000 IOPS RAID0 XFS OS: AL2023 Kernel: v7.3-rc1 Database: PostgreSQL 18.4 Workload: pgbench simple-update, 1024 clients, 96 threads, 1200s Results (average of 3 runs, TPS): Config Avg TPS % vs baseline v7.3-rc1 baseline (vm.defrag_mode=0) 58,602 - v7.3-rc1 + this patch (vm.defrag_mode=0) 157,246 +168.3% v7.3-rc1 baseline (vm.defrag_mode=1) 109,012 - v7.3-rc1 + this patch (vm.defrag_mode=1) 157,778 +44.7% Link: https://lore.kernel.org/20261001082152.2879289-1-dipiets@amazon.it Link: https://lore.kernel.org/all/20260403193535.9970-1-dipiets@amazon.it/T/#t [v1] Link: https://lore.kernel.org/linux-mm/20260420161404.642-1-dipiets@amazon.it/T/#u [v2] Link: https://lore.kernel.org/all/20260710143437.12379-1-dipiets@amazon.it/T/#u [v3] Link: https://lore.kernel.org/all/20260904115629.3993331-1-dipiets@amazon.it/T/#u [v4] Link: https://lore.kernel.org/all/20260911142102.2294202-1-dipiets@amazon.it/T/#u [v5] Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") Signed-off-by: Salvatore Dipietro Signed-off-by: Andrew Morton Acked-by: Vlastimil Babka (SUSE) Acked-by: Zi Yan Reviewed-by: Johannes Weiner Reviewed-by: Christoph Hellwig Cc: David Hildenbrand Cc: Michal Hocko Cc: Matthew Wilcox Cc: Dave Chinner Cc: Ritesh Harjani Cc: Dmitry Ilvokhin Cc: Hazem Mohamed Abuelfotoh Cc: Ali Saidi Cc: Geoff Blake Cc: Christian Brauner Cc: Cc: Darrick J. Wong Cc: Brendan Jackman Cc: Cc: Suren Baghdasaryan Cc: "Garg, Shivank" introduced high-order folio allocations in the iomap buffered write path. When memory is fragmented, each failed costly-order allocation enters __alloc_pages_slowpath() which runs direct reclaim, direct compaction and drain_all_pages(), causing a 0.38x throughput drop on PostgreSQL pgbench (simple-update) with 1024 clients on a 96-vCPU arm64 system. The root issue is that direct reclaim and direct compaction are too expensive for hot allocation paths that have fallbacks to smaller allocations. __filemap_get_folio_mpol() already marks higher-order allocations with __GFP_NORETRY | __GFP_NOWARN, signalling that the caller can handle failure. However, the page allocator still enters the full blocking slowpath for costly orders with __GFP_NORETRY, which is unnecessarily aggressive when the caller will simply retry at a lower order. For costly-order allocations with __GFP_NORETRY, clear __GFP_DIRECT_RECLAIM at the very start of the slowpath, before can_direct_reclaim, can_compact and the nofail checks are evaluated. This makes the entire slowpath treat the request as non-blocking: no direct reclaim, no direct compaction and no drain_all_pages() IPI across every CPU. Reclaim and compaction move to the background instead: kswapd is still woken for reclaim, and it wakes kcompactd for defragmentation. The system keeps its long-term health while the latency-critical direct allocation path no longer stalls. Allocations that also request __GFP_THISNODE are exempted. That flag pairing identifies the local-node-first THP attempt issued by alloc_pages_mpol() (mempolicy.c), which relies on direct compaction to form transparent huge pages. Clearing __GFP_DIRECT_RECLAIM makes these allocations reach the !can_direct_reclaim bailout, which since commit 4c0ed883e051 ("mm/page_alloc: fix defrag_mode for non-reclaimable allocations") drops ALLOC_NOFRAGMENT and retries instead of failing when defrag_mode is on. With vm.defrag_mode=1 a __GFP_NORETRY allocation could therefore succeed by fragmenting another migratetype's pageblock. That is the wrong trade for a caller that has already communicated it can handle failure and has a cheap lower-order fallback, so exclude __GFP_NORETRY from the relaxation. Signed-off-by: Sasha Levin --- mm/page_alloc.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ddffc7c8430e8..8714425ffe84e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4791,10 +4791,10 @@ static inline struct page * __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, struct alloc_context *ac) { - bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM; - bool can_compact = can_direct_reclaim && gfp_compaction_allowed(gfp_mask); - bool nofail = gfp_mask & __GFP_NOFAIL; const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER; + bool can_direct_reclaim; + bool can_compact; + bool nofail; struct page *page = NULL; unsigned int alloc_flags; unsigned long did_some_progress; @@ -4809,6 +4809,18 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, bool can_retry_reserves = true; unsigned long alloc_start_time = jiffies; + /* + * Costly __GFP_NORETRY callers have a cheap fallback, so don't stall + * them in reclaim or compaction. __GFP_THISNODE callers are exempt. + */ + if (costly_order && (gfp_mask & __GFP_NORETRY) && + !(gfp_mask & __GFP_THISNODE)) + gfp_mask &= ~__GFP_DIRECT_RECLAIM; + + can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM; + can_compact = can_direct_reclaim && gfp_compaction_allowed(gfp_mask); + nofail = gfp_mask & __GFP_NOFAIL; + if (unlikely(nofail)) { /* * Also we don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM, @@ -4925,8 +4937,11 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, * Reclaim/compaction cannot run, so defrag_mode's strategy * of enforcing ALLOC_NOFRAGMENT cannot be fulfilled. Allow * fallbacks rather than failing the allocation outright. + * Not for __GFP_NORETRY: those have a cheap lower order + * fallback, so failing beats fragmenting. */ if (defrag_mode && (alloc_flags & ALLOC_NOFRAGMENT) && + !(gfp_mask & __GFP_NORETRY) && (gfp_mask & __GFP_KSWAPD_RECLAIM)) { alloc_flags &= ~ALLOC_NOFRAGMENT; goto retry; -- 2.53.0