From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D3C9D2857D5; Tue, 6 May 2025 17:40:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746553237; cv=none; b=Est+ZLbNz3HX84Xj//SfL/RzOAzNoM8DujyuH4ybdh61CnvpLVyr/v00AUbb0wgwXRvWZSGBoJUGadMFdJdVcFkF27BwXZ9cu+swUGCPqybTlt8ftOj2svEcGNG45kPUmgr73WQQsXY2ca6RjSi/69KwmkoJGic5VQmghLxcoKo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746553237; c=relaxed/simple; bh=h9XuZ1xhYzE1KM9SZa4s375E1QtL5TdMDJJnXBefZ/A=; h=Message-ID:Subject:From:To:Cc:Date:Content-Type:MIME-Version; b=iLxQm/O4m+nsnqhsw6o7saIX9X9c2nVfHSrusPBqApw6gIwEzZVkX6DJmz6qoYn8s7XfbUN+7Keh3Sp5KI2k6c2p/yNCQyqiO6nucIY81xrVWITSgjB4ouqLztMNcJqLLl7OglKkViBxIHxDItg7XWkrP7rr1yB2l5DdnDIQdO0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q/dF5YiQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Q/dF5YiQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 931E1C4CEEF; Tue, 6 May 2025 17:40:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746553237; bh=h9XuZ1xhYzE1KM9SZa4s375E1QtL5TdMDJJnXBefZ/A=; h=Subject:From:To:Cc:Date:From; b=Q/dF5YiQYZY8TOstGtIrUVJzfBF23eRASxuIA8DmG5JWbBY3Y2+7+zg+F6RGW3+dS esdVIz4xWfc8TkL6L/+GA94BN2ZZ3guJAv/4DIvRHkeNbA1znRZOs+gx7LIxJsrcP1 eBz9U1LMU0uq53W0CM1+8Y+5Po65F0/JrjHuPFWj9uETOEswPU+j1YxFihRKzpjyvC 0zuV/b/N5YWYrJwmqm+3Iakw0J2sCCjtkhf/HHkMmui89PMLADBCdPK0EvtaXi/U67 m66C9GWyak7iag0QNMSgr1ETE3cxUqwuUQRCUHkuWXIqhnbsphMCklgGJVZdgVPu9Y Z0LH2IEh7PNWA== Message-ID: <370dd4ae06d44f852342b7ee2b969fc544bd1213.camel@kernel.org> Subject: performance r nfsd with RWF_DONTCACHE and larger wsizes From: Jeff Layton To: linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Cc: Chuck Lever , Mike Snitzer , Trond Myklebust , Jens Axboe , Chris Mason , Anna Schumaker Date: Tue, 06 May 2025 13:40:35 -0400 Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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Those add a module param that make all reads and writes use RWF_DONTCACHE. I had one host that was running knfsd with an XFS export, and a second that was acting as NFS client. Both machines have tons of memory, so pagecache utilization is irrelevant for this test. I tested sequential writes using the fio-seq_write.fio test, both with and without the module param enabled. These numbers are from one run each, but they were pretty stable over several runs: # fio /usr/share/doc/fio/examples/fio-seq-write.fio wsize=3D1M: Normal: WRITE: bw=3D1034MiB/s (1084MB/s), 1034MiB/s-1034MiB/s (1084MB/= s-1084MB/s), io=3D910GiB (977GB), run=3D901326-901326msec DONTCACHE: WRITE: bw=3D649MiB/s (681MB/s), 649MiB/s-649MiB/s (681MB/s-681= MB/s), io=3D571GiB (613GB), run=3D900001-900001msec DONTCACHE with a 1M wsize vs. recent (v6.14-ish) knfsd was about 30% slower. Memory consumption was down, but these boxes have oodles of memory, so I didn't notice much change there. Chris suggested that the write sizes were too small in this test, so I grabbed Chuck's patches to increase the max RPC payload size [2] to 4M, and patched the client to allow a wsize that big: wsize=3D4M: Normal: WRITE: bw=3D1053MiB/s (1104MB/s), 1053MiB/s-1053MiB/s (1104MB= /s-1104MB/s), io=3D930GiB (999GB), run=3D904526-904526msec DONTCACHE: WRITE: bw=3D1191MiB/s (1249MB/s), 1191MiB/s-1191MiB/s (1249MB= /s-1249MB/s), io=3D1050GiB (1127GB), run=3D902781-902781msec Not much change with normal buffered I/O here, but DONTCACHE is faster with a 4M wsize. My suspicion (unconfirmed) is that the dropbehind flag ends up causing partially-written large folios in the pagecache to get written back too early, and that slows down later writes to the same folios. I wonder if we need some heuristic that makes generic_write_sync() only kick off writeback immediately if the whole folio is dirty so we have more time to gather writes before kicking off writeback? This might also be a good reason to think about a larger rsize/wsize limit in the client. I'd like to also test reads with this flag, but I'm currently getting back that EOPNOTSUPP error when I try to test them. [1]: https://lore.kernel.org/linux-nfs/20250220171205.12092-1- snitzer@kernel.org/ [2]: https://lore.kernel.org/linux-nfs/20250428193702.5186-15- cel@kernel.org/ --=20 Jeff Layton