From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pdx-out-005.esa.us-west-2.outbound.mail-perimeter.amazon.com (pdx-out-005.esa.us-west-2.outbound.mail-perimeter.amazon.com [52.13.214.179]) (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 C0B6B4AB1BB; Thu, 1 Oct 2026 08:22:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=52.13.214.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790842974; cv=none; b=DAhj2phcObYux8J73d1JjHbBm6R+N1iLS84/UO3KzeWuX4b3aQ7H678OnnLsNWgl9ss+XYeaj7TRr3FEu76VGZzwUsJ512+GTT4phC3XxjDk4nIytsBJ3aZAj8jKipIDoeGMuFkbGplS6EOQdxJ7Kl/P9staPutAegfjQ5gHSCQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790842974; c=relaxed/simple; bh=dssCCR8+SfXy1LqmvrukStNfjE8hHWa/j5bJ9Ck8GDg=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=O4eJmKjLJoVT4pAFhIPLfnnMVVSpJ7LveW4DR30xg9hGE+Crtn9qQjZI2dZZ3A40hApR+6gdFkMl5Pat8uHGtZbZzDKt/VEZ3xjvS6lYpKqk0re2O16tXVlOck2fFfVuMXXvaDb6eT3+vNh/o68ngVch1mgcYZWik+h9sKajaWw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.it; spf=pass smtp.mailfrom=amazon.it; dkim=pass (2048-bit key) header.d=amazon.it header.i=@amazon.it header.b=n1Pcd1Mu; arc=none smtp.client-ip=52.13.214.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.it Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.it Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.it header.i=@amazon.it header.b="n1Pcd1Mu" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.it; i=@amazon.it; q=dns/txt; s=amazoncorp2; t=1790842955; x=1822378955; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=pMNM3ezMCf72JOW7w9gZHwjUf5zgBeoBXpZHv9GCuqo=; b=n1Pcd1MuahMe2XJoDfvyq56CzTiJttDAHXvU9vxl/9A/uqhl9fVzrBpS JkRhPP2ruNTI9q+Jz3KTc54gwzYuCrIebJDcEVKBqf2mvzvl7TprjAQ8B JmmoQS4ufZk3MeYS2tqTeOMteFXmV9MPM3+lAX6pbuERrGFfOyo6Ywyu6 Ppgmqh+BXt/6bzofMClPMGMjcFylC/85wRkCjA8Lj3f4jWCznXIfq9Oij PGK9zFgfTZQo02EWxgPJKQRrEzIFEsKHXWTA6asnZRZ28nku2prdVVSWO WEq29U02AujdncqJpC6GR/hWTVlKkPYZeVezGR4HvIFdsiMBvSQP4XV2x g==; X-CSE-ConnectionGUID: tST3wUViQXKbYg0FlT4gLg== X-CSE-MsgGUID: CeFmmwQxQA+xgUJufVb77Q== X-IronPort-AV: E=Sophos;i="6.27,134,1787011200"; d="scan'208";a="30088223" Received: from ip-10-5-9-48.us-west-2.compute.internal (HELO smtpout.naws.us-west-2.prod.farcaster.email.amazon.dev) ([10.5.9.48]) by internal-pdx-out-005.esa.us-west-2.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2026 08:22:24 +0000 Received: from EX19MTAUWB001.ant.amazon.com [205.251.233.104:9288] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.21.22:2525] with esmtp (Farcaster) id d7332f4c-b57b-4f23-8dac-76fc3c82d408; Thu, 1 Oct 2026 08:22:24 +0000 (UTC) X-Farcaster-Flow-ID: d7332f4c-b57b-4f23-8dac-76fc3c82d408 Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWB001.ant.amazon.com (10.250.64.248) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.49; Thu, 1 Oct 2026 08:22:23 +0000 Received: from dev-dsk-dipiets-1b-77b833da.eu-west-1.amazon.com (10.253.66.177) by EX19D001UWA001.ant.amazon.com (10.13.138.214) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.49; Thu, 1 Oct 2026 08:22:20 +0000 From: Salvatore Dipietro To: CC: , , , , , , , , , , , , , , , , , , , , , , , "David Hildenbrand" , Christoph Hellwig , "Dmitry Ilvokhin" , Brendan Jackman Subject: [PATCH v6] mm/page_alloc: avoid direct reclaim and compaction for costly __GFP_NORETRY allocations Date: Thu, 1 Oct 2026 08:21:51 +0000 Message-ID: <20261001082152.2879289-1-dipiets@amazon.it> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D035UWA003.ant.amazon.com (10.13.139.86) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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/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") Cc: stable@vger.kernel.org Cc: Andrew Morton Cc: Vlastimil Babka Cc: David Hildenbrand Cc: Michal Hocko Cc: Johannes Weiner Cc: Matthew Wilcox Cc: Christoph Hellwig Cc: Dave Chinner Cc: Ritesh Harjani Cc: Zi Yan Cc: Dmitry Ilvokhin Cc: linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-xfs@vger.kernel.org Cc: linux-kernel@vger.kernel.org Acked-by: Vlastimil Babka (SUSE) Acked-by: Zi Yan Reviewed-by: Johannes Weiner Reviewed-by: Christoph Hellwig Signed-off-by: Salvatore Dipietro --- 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 12fac9084c48..64d09964ca77 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4784,10 +4784,10 @@ 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; @@ -4802,6 +4802,18 @@ __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, @@ -4918,8 +4930,11 @@ __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; base-commit: cee9395acd8043be0644b25c34bfa86623f2b935 -- 2.50.1 AMAZON DEVELOPMENT CENTER ITALY SRL, viale Monte Grappa 3/5, 20124 Milano, Italia, Registro delle Imprese di Milano Monza Brianza Lodi REA n. 2504859, Capitale Sociale: 10.000 EUR i.v., Cod. Fisc. e P.IVA 10100050961, Societa con Socio Unico