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 B51CB1A6806; Wed, 22 Jul 2026 12:35:57 +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=1784723758; cv=none; b=jg0pXiX1jvzSRcg62jtTKY77w/UiFHLhBwcznwiuiPw7K4Ygz4lhCvF9nDffJcNKhFjKo1v0iVRMWw0hpa0eYR2B0sMx7PAd4CvOZgH34lb6oD/yl1ygxhcsEseQvGzhleuQaOJVLDcXYz9kBVxHGyimiMfg3UiSKXWwBM3Uybg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784723758; c=relaxed/simple; bh=jGMB6iE9lxJe5nKtxoXNDfrLRI4gR7M3ptjh6wD6/WI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ayLc+oGGCXmHSIxirEdTDXtqoxf3l1lxLfNqju/5ZF5XX6cWMnZ97QAmVNITCv1up7ShQuI+JgcKkCfHGl9QGlHJyKgdOoIx+gY82QTVICL8BrTg64LLd7eq5gmRR8jlXxIzHQvbiHCPqAZLMPmH8KEH24quz+BBjxPFov/zv/k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HyIzudcH; 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="HyIzudcH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 003651F000E9; Wed, 22 Jul 2026 12:35:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784723757; bh=2Jd1GANGwM+PXpSKQ+CRzq/E6/EDkcfhb0HgkIh9hJw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HyIzudcHgwOZMnwvnVThzTbiSoYQgWKiZ7BSA5Nn93yO5ZwK9lei72TD5EsIyvErW IBdApPWF/AFiQzqCq6bhBEkYP7OBWar0qnqBy6tDn0UVNS/UQDyr4Tr49g9ife1kGG PjgiL6sCmL5DZQR2/qRy3V6BSx7RPXHJ9QG9Tsm6etiWSMv+PcWkqBXCseFJR0wKjC 2EiLaTBxgsBcsTcEPY6IrLBGKcD5HpS4iTaK+Ep2QcVcZ/xQT6/7WZKjkyW0RbAhX4 2QTChyiE4YyE/kBFyhpYK/tppcL5nZQpL7EuRWN9qfuuxq3FtATsfFiTdrsAKf0uIE phOj7bGLdPLfQ== Message-ID: <7ddb704c-76a9-4071-8969-06fa1403eb07@kernel.org> Date: Wed, 22 Jul 2026 14:35:51 +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 v3] mm/page_alloc: avoid direct compaction for costly __GFP_NORETRY allocations Content-Language: en-US To: Salvatore Dipietro , hannes@cmpxchg.org, willy@infradead.org Cc: abuehaze@amazon.com, akpm@linux-foundation.org, alisaidi@amazon.com, blakgeof@amazon.com, brauner@kernel.org, dgc@kernel.org, dipietro.salvatore@gmail.com, djwong@kernel.org, hch@infradead.org, jackmanb@google.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, mhocko@suse.com, ritesh.list@gmail.com, stable@vger.kernel.org, surenb@google.com, ziy@nvidia.com References: <20260714120204.542300-1-dipiets@amazon.it> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/14/26 14:02, Salvatore Dipietro wrote: > > Hi Johannes, Matthew, > > Thank you both for the alternative proposals. I've tested both > approaches on the same test environment used for v3. > > Results (4 runs each): > > Config Avg TPS % vs Baseline > -------------------------------------------------------- > baseline (no patch) 70,735 - > Johannes' approach 156,908 +121.8% > Matthew's approach 70,145 -0.8% (within noise) > > > Johannes' approach (clearing __GFP_DIRECT_RECLAIM early in the > slowpath for costly __GFP_NORETRY) delivers the same ~2.2x speedup > as v3, as expected - it prevents the entire direct reclaim and > compaction machinery from running for these opportunistic allocations. AFAICS both your v3 and the implemented Johannes' suggestion effectively make all the compact_first logic dead code - at least for the intended THP use case based on costly_order. It will only continue to do something for the non-movable order>0 case. So that's a significant change which will not show up in your results, but might affect other workloads (I'd expect mainly by having fewer THPs). > Matthew's filemap.c approach does not help in this workload. The > reason is that the first allocation attempt at max order still carries > __GFP_DIRECT_RECLAIM and enters the slowpath with direct compaction > enabled. The __GFP_DIRECT_RECLAIM clearing only takes effect for > subsequent lower-order attempts in the fallback loop, but the costly > compaction has already executed on the first try. > > Let me know if you have any other variant you want me to test, > or if I should prepare a v4 based on Johannes' suggestion. > > This is what I tested for Johannes' approach: > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a63733dac659..6e960c969e67 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4733,10 +4733,10 @@ 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; > @@ -4751,6 +4751,20 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > bool can_retry_reserves = true; > unsigned long alloc_start_time = jiffies; > > + /* > + * Costly __GFP_NORETRY allocations are opportunistic: the caller > + * can fall back to smaller orders. Don't stall on direct reclaim > + * or compaction; clearing __GFP_DIRECT_RECLAIM makes the entire > + * slowpath treat this as a non-blocking request. kswapd will wake > + * kcompactd as needed for background defragmentation. > + */ > + if (costly_order && (gfp_mask & __GFP_NORETRY)) > + 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, > > > Thanks, > Salvatore > > > > > > 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 > > >