From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pdx-out-008.esa.us-west-2.outbound.mail-perimeter.amazon.com (pdx-out-008.esa.us-west-2.outbound.mail-perimeter.amazon.com [52.42.203.116]) (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 40652495022; Fri, 4 Sep 2026 11:57:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=52.42.203.116 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788523031; cv=none; b=FPO7BX4xrt3YBHK9HIeNJgwUR91nvBsVaIMY9rZMIFQMJo3I0Y+7HoUZeWY4mQ6I8ZZvDAlONdtqyT5xaucrz+UOnRA010rc0mfsgVCjNo2sU1jfHSDmZkyuJrzzOPkX5z8Yw8PJs23+mOYGuxi3X7CJClqgwS3gThkWD8oUlwU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788523031; c=relaxed/simple; bh=KCaZ/7WPMv1EdIHUVBFLlhu9macY3vqtcdBoHCcEwpU=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=uTM8zBAoPYos05GuTFMp9UEgRBYMkeoGhS0Lj7L4OtPvCW9k/dKX5L0wRgHgRUgM2rPapHjMjFP0fOPriy56jTqzscOtaykyYFRlFegA5cbl55vyLT1/lDJJ/U1WTXFn1Qu6rzP3kHW4dyCB0WUA3lpq87wssMCYloamJcnd+LQ= 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=fxr57ki3; arc=none smtp.client-ip=52.42.203.116 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="fxr57ki3" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.it; i=@amazon.it; q=dns/txt; s=amazoncorp2; t=1788523028; x=1820059028; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=SOjD2ZTgpTZf/InCnmcmr36L5a0mZycSlAjIYBy93Ps=; b=fxr57ki3c516dtzG+fuseZO5S6xSjMpG5UdTBPTK4X19gu0zl82BZnZC z06PQwn8jnR7F2P0pzy20JJOGBmKv72Ca8++l0MbDfbZwKLxwugbBzTJa akzgqHM4R8YRbZcBcKzZqbWFthCVCITyBlkOHo8tnKZtzd4NrAy2ZPggA acYY0uTPZ77AxRo8zpDk3fEZfQ2B4D/LQB2uUNdsDrreThQ2jRrZ/U/6m CJpDqcItlgVwVRbmjKPGP3Rnluu45PqKUsdjvHG04E4mev7mK3MkEAOUB kBn4gBuZ0OGOHRgwQqt6LngTRqqWFYSimMjpQ3svuDPcf99yMOXUyjzH5 w==; X-CSE-ConnectionGUID: iAXNTirhSJaOs9v4vT772A== X-CSE-MsgGUID: O4XTqRyDTUOIEtI3JKf8Ig== X-IronPort-AV: E=Sophos;i="6.25,262,1779148800"; d="scan'208";a="27847546" Received: from ip-10-5-12-219.us-west-2.compute.internal (HELO smtpout.naws.us-west-2.prod.farcaster.email.amazon.dev) ([10.5.12.219]) by internal-pdx-out-008.esa.us-west-2.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Sep 2026 11:57:03 +0000 Received: from EX19MTAUWA001.ant.amazon.com [205.251.233.236:15535] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.60.115:2525] with esmtp (Farcaster) id b4a5571f-f245-4ceb-b67a-51094f9b8089; Fri, 4 Sep 2026 11:57:02 +0000 (UTC) X-Farcaster-Flow-ID: b4a5571f-f245-4ceb-b67a-51094f9b8089 Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWA001.ant.amazon.com (10.250.64.218) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.45; Fri, 4 Sep 2026 11:57:02 +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 15.2.2562.46; Fri, 4 Sep 2026 11:56:57 +0000 From: Salvatore Dipietro To: , CC: , , , , , , , , , , , , , , , , , , , , , , Vlastimil Babka , David Hildenbrand , Christoph Hellwig , Brendan Jackman Subject: [PATCH v4] mm/page_alloc: avoid direct compaction for costly __GFP_NORETRY allocations Date: Fri, 4 Sep 2026 11:56:28 +0000 Message-ID: <20260904115629.3993331-1-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: EX19D031UWC003.ant.amazon.com (10.13.139.252) 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 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 compaction is 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 attempts full direct compaction 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. kswapd (and in turn kcompactd) is still woken further down for background defragmentation, so compaction keeps working for long-term system health while being removed from the latency-critical direct allocation path. 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. 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 baseline (no patch) 59,408 - With this patch 155,409 +161.6% 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] 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: linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-xfs@vger.kernel.org Signed-off-by: Salvatore Dipietro --- v4: Clear __GFP_DIRECT_RECLAIM early in the slowpath and exempt __GFP_THISNODE so THP attempt keeps using direct compaction v3: Move to mm/page_alloc.c, wake kcompactd instead of avoiding it v2: Move from fs/iomap/buffered-io.c to mm/filemap.c v1: Avoid compaction in iomap folio allocation mm/page_alloc.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 12fac9084c48..542c2ec31061 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, -- 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