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Sat, 04 Apr 2026 10:24:50 -0700 (PDT) Received: from pve-server ([49.205.216.49]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c76c657e703sm7990160a12.22.2026.04.04.10.24.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 04 Apr 2026 10:24:49 -0700 (PDT) From: Ritesh Harjani (IBM) To: Matthew Wilcox , Salvatore Dipietro Cc: linux-kernel@vger.kernel.org, alisaidi@amazon.com, blakgeof@amazon.com, abuehaze@amazon.de, dipietro.salvatore@gmail.com, stable@vger.kernel.org, Christian Brauner , "Darrick J. Wong" , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/1] iomap: avoid compaction for costly folio order allocation In-Reply-To: Date: Sat, 04 Apr 2026 22:17:33 +0530 Message-ID: <5x66n04a.ritesh.list@gmail.com> References: <20260403193535.9970-1-dipiets@amazon.it> <20260403193535.9970-2-dipiets@amazon.it> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 86D6A40005 X-Stat-Signature: th1bzj75b649rineyu9qi6hqb9nppbpg X-HE-Tag: 1775323492-857592 X-HE-Meta: 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 22vAqydB 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Matthew Wilcox writes: > On Fri, Apr 03, 2026 at 07:35:34PM +0000, Salvatore Dipietro wrote: >> Commit 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") >> introduced high-order folio allocations in the buffered write >> path. When memory is fragmented, each failed allocation triggers >> compaction and drain_all_pages() via __alloc_pages_slowpath(), >> causing a 0.75x throughput drop on pgbench (simple-update) with >> 1024 clients on a 96-vCPU arm64 system. >> >> Strip __GFP_DIRECT_RECLAIM from folio allocations in >> iomap_get_folio() when the order exceeds PAGE_ALLOC_COSTLY_ORDER, >> making them purely opportunistic. > > If you look at __filemap_get_folio_mpol(), that's kind of being tried > already: > > if (order > min_order) > alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN; > > * %__GFP_NORETRY: The VM implementation will try only very lightweight > * memory direct reclaim to get some memory under memory pressure (thus > * it can sleep). It will avoid disruptive actions like OOM killer. The > * caller must handle the failure which is quite likely to happen under > * heavy memory pressure. The flag is suitable when failure can easily be > * handled at small cost, such as reduced throughput. > > which, from the description, seemed like the right approach. So either > the description or the implementation should be updated, I suppose? > > Now, what happens if you change those two lines to: > > if (order > min_order) { > alloc_gfp &= ~__GFP_DIRECT_RECLAIM; > alloc_gfp |= __GFP_NOWARN; > } Hi Matthew, Shouldn't we try this instead? This would still allows us to keep __GFP_NORETRY and hence light weight direct reclaim/compaction for atleast the non-costly order allocations, right? if (order > min_order) { alloc_gfp |= __GFP_NOWARN; if (order > PAGE_ALLOC_COSTLY_ORDER) alloc_gfp &= ~__GFP_DIRECT_RECLAIM; else alloc_gfp |= __GFP_NORETRY; } -ritesh > > Do you recover the performance?