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 97E7B4756D5; Fri, 11 Sep 2026 16:32:11 +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=1789144338; cv=none; b=A3yP21OqTtZVeYoMCxUNa3/PcRoc41nLPCy85Qd5/5W0jnPsFg0LzAUlGCzUEzp+q9wToy3FHrHuIVo9xaTTX/Rjz+o63M917FRKKLaLTUugI2ZvNfQg6PfXCCMlbz3hymtJkgKy0ypPtDFEP9+kMvCYjJmlJOGw5+wIpA2DqLo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789144338; c=relaxed/simple; bh=qJkCbqia+PyvtsUo7qKbKv2ZL6lFALKHQ+NVremMqJY=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=MqSuvDvbaN9DzhelTi6TZUE++iKQS5/Ft6AStUsBKJ3P/4lIPo+67k5pmKaR8A9EDBwIn+zoQSajPyh4NTBaeE3TOi5ifHzKBDuCKaK3N1zKpxBDEDj/kgfbMimW5tBenWBxIS19llSzdS9APCtbcy8CNMdIFzPErATVKBz6XhE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=gy1m7qOG; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="gy1m7qOG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17C3D1F00893; Fri, 11 Sep 2026 16:32:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789144330; bh=j9rqeVVJkLJL7hyeN+ZhuUze7JPnMyhzvchT9akDlcM=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=gy1m7qOGyWRZPMTSfQJX9GQn8OMxswkKp0FjsuSudkheza3eMi6XvIr048H2mPW3M PL8rI73VtGnov+Hua7Sm836ztsrYcARh0SXYdWOwul2HOk/YsGB76Z9LE6hNVa3jgU bkeKe0wZLVavneFVz57sps8mALXwElCoNhR6bGFA= Date: Fri, 11 Sep 2026 09:32:09 -0700 From: Andrew Morton To: Salvatore Dipietro Cc: , , , , , , , , , , , , , , , , , , , , , , Vlastimil Babka , David Hildenbrand , Christoph Hellwig , Brendan Jackman Subject: Re: [PATCH v5] mm/page_alloc: avoid direct compaction for costly __GFP_NORETRY allocations Message-Id: <20260911093209.d9181d5950778897935f6bcb@linux-foundation.org> In-Reply-To: <20260911142102.2294202-1-dipiets@amazon.it> References: <20260911142102.2294202-1-dipiets@amazon.it> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 11 Sep 2026 14:21:02 +0000 Salvatore Dipietro wrote: > 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, suppress direct reclaim > for the whole slowpath by computing can_direct_reclaim (and hence > can_compact) as false. The !can_direct_reclaim check near the top of > the slowpath then short-circuits to nopage: 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. __GFP_NOFAIL is exempted as well, so a > must-not-fail allocation is never made to fail. > > 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 > AL2023 stock 6.1 kernel (pre-5d8edfb900d5) 136,942 n/a > v7.3-rc1 baseline (no patch) 59,408 - > v7.3-rc1 + this patch 161,994 +172.7% > > The patch fully recovers the pre-5d8edfb900d5 performance, bringing > throughput back above the pre-regression level and well clear of the > ~59k baseline. The AL2023 6.1 row runs a kernel that predates commit > 5d8edfb900d5 ("iomap: Copy larger chunks from userspace"), so it is not > directly comparable, but it shows the pre-regression level and confirms > that the ~59k baseline is the anomaly and not the norm. Thanks, I'll update mm.git's mm-hotfixes-unstable branch with this. > v5: Derive the decision into a local flag instead of mutating gfp_mask The acks from vbabka, hannes and hch were dropped. Fair enough - that's always a hard call. Sashiko is worried: https://sashiko.dev/#/patchset/20260911142102.2294202-1-dipiets@amazon.it That's different from Sashiko's v4 complaints: https://sashiko.dev/#/patchset/20260904115629.3993331-1-dipiets@amazon.it does any of this look real?