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 32FB144A3E8; Fri, 2 Oct 2026 08:23:54 +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=1790929436; cv=none; b=VS40usVFMXOpYwp3tPgVpaSgzAvR51qwsLru0v3m49f1P8TCdjYVg85bdowVawFsZNB/DoyX+p/+lWS55DiydBTOer9Ua/ZvFhzvuZbzGOCYZEpCbMFDCWkMjas/AYUi+pFFU4pqUV67TWmRyytX5w8CdlfuTV1677eqHc2WNJI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790929436; c=relaxed/simple; bh=Uem7JOMRycuTBxtKaZIShzS/ClMiUI+0+yS3WdnGVLw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uij1N6KgrFWLeyg9vm1zG1pwYCJeaBH1c6Y/hhulyG/iP1IHB2XpWBbJy96Fk4onEJFgEQmhTbETu6KTXJsv5024wFGQNnp9Y4KkhrHwWl/LK/GzY8CiRyfoR0sHtUDDiiks5OEphJz/IYuYemGyKErPgQ1YIB7P5Dx80bvfC9Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=m39OTSXG; 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="m39OTSXG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 588551F000FF; Fri, 2 Oct 2026 08:23:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790929434; bh=EscagxTaRgsbT7pEbj1a/c/B7oDWZ/qp9i/g3XXY2T8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=m39OTSXGNZNIqCEztgvYpbKdbg8exALPQw7LXuaZ+cFC4pTdZYLSKC2Zdjd81Vyer eZpFzbESNoK57ZUzT63Kbqvgt1CMyurYUx2euQpsisN/d4NC/346wAtZsoptWrU4Bx uRX4gEsirlSzXf+lc+Rns6jlQ7EWFJcNt9l7zBzO/7jjfAGfLlses1qCqZ2PnXXuYW HsohxPZh4YLf6b2zK1D0YtNlqhIZJHYa8PyNjgE2x5N+oRAcrUXbuEmqvxa4E75PVC dpN563eX06NOCoyUTkrJGWoANofJdSgpOtzf+lUCyE0JhqCyCjG6ZGZGK36cUa9/jQ Dnw4JlCRv97UQ== Message-ID: <42d1a163-3502-49b8-9a27-7df9d06eee64@kernel.org> Date: Fri, 2 Oct 2026 10:23:47 +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 v6] mm/page_alloc: avoid direct reclaim and compaction for costly __GFP_NORETRY allocations Content-Language: en-US To: Andrew Morton , Salvatore Dipietro Cc: linux-kernel@vger.kernel.org, hch@infradead.org, abuehaze@amazon.com, alisaidi@amazon.com, blakgeof@amazon.com, brauner@kernel.org, dgc@kernel.org, dipietro.salvatore@gmail.com, djwong@kernel.org, hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, mhocko@suse.com, ritesh.list@gmail.com, rvvandan@amazon.com, stable@vger.kernel.org, surenb@google.com, willy@infradead.org, ziy@nvidia.com, David Hildenbrand , Christoph Hellwig , Dmitry Ilvokhin , Brendan Jackman References: <20261001082152.2879289-1-dipiets@amazon.it> <20261001182942.ce99faa753fb9d9bd2efec1e@linux-foundation.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/2/26 03:29, Andrew Morton wrote: > On Thu, 1 Oct 2026 08:21:51 +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 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. >> Since it expands the impact of a pre-existing bug of nonblocking allocation eating reserves [1] it shouldn't proceed to mainline without a fix for that (Johannes posted it there but the review discussion got stalled). > Thanks, I'll update mm-hotfixes to this version. I've also argued for not handling it as a hotfix [2] [1] https://lore.kernel.org/all/9f415dc7-adad-4161-b20d-7c3173f50ff3@kernel.org/ [2] https://lore.kernel.org/all/c6e2c1e1-a285-406e-a2b6-c09e05df91d8@kernel.org/ > Here's what changed: > > --- a/mm/page_alloc.c~mm-page_alloc-avoid-direct-reclaim-and-compaction-for-costly-__gfp_noretry-allocations > +++ a/mm/page_alloc.c > @@ -4930,8 +4930,11 @@ retry: > * 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; > _ >