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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 Message-ID: References: <20260403193535.9970-1-dipiets@amazon.it> <20260403193535.9970-2-dipiets@amazon.it> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260403193535.9970-2-dipiets@amazon.it> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: DE8BF40003 X-Stat-Signature: szxy9yorhgrkzuqp8uzhdunzumysxfca X-Rspam-User: X-HE-Tag: 1775276112-815794 X-HE-Meta: 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 78WHXmxd AQvwdwBv73qMmw5snTjaYntFX6VznRNi/k17ZdQ1wUpfOcP81b6CF5is8hhraaN+bq+tOik+tvQq2mFJsH+cvj0Pf7UJ1Qb0tOlPVkDIZqgzK7oV/5v6QC+piUwDdF+dwQ3/m6dkG3U79i8WLKbdnZl7NGJlR1vnccxoodKA140DFuKAdaptS1Vu4xNdRMBtH1Mgrg4GmVNI8AIDymT9+1mcxyKYp8DAnLrO5+nM+dWgU6kW27Gc0y5dj6n7kSc0+jiiz/b9DVCL7zr++FAOBamF62Ip8QuLywqTsT3qnmkQqyKVwo4uKtjcQf7IbUmwp4VPV Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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; } Do you recover the performance?