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 41DD428643B; Tue, 6 May 2025 18:30:05 +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=1746556207; cv=none; b=dOHU98odUtzNtQpg82/i5WGtIcFLgjMSa1ZFo2euxplvzYLMYhcdajLDv7cVp+Yt7cT3SC3IhjGOCks5Qkok6LAdp9bQ996W9UTBCsQ/05Y6TtYzOJgI6uY8K08Seb4CLnP+tF0hdpB8XtF9GIW8Vm3m5S57VJAmhDdXOwgTgTA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746556207; c=relaxed/simple; bh=5T4zXrMD4XeSy/waZcahRkYiRVuVEIdKStQhCfFz7oI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=nN9cR44VMcNuQjmSgB5/BJ8+g45TWqVTU/fcXMH8x/BtUW8GRTMQ1AuBe3JBUwzW7bOM93er8/tXLGnetYtI3bJo0RjjJD1H6zcCiy/y3P61rlOtQzc3XSOjAHTHMkyzD8wSYuUqewLs+n5fMLsFyUt1p+GwofrWc6GGePNAluE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pE2NGvA7; 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="pE2NGvA7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15EA1C4CEE4; Tue, 6 May 2025 18:30:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746556205; bh=5T4zXrMD4XeSy/waZcahRkYiRVuVEIdKStQhCfFz7oI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=pE2NGvA7M3tbVXTV4PwHakBn1k9/LGml5Z/okOs/KNiZyJCUq/ndwBBHP/L3kvusO CSkY+o6ha/moBArEqqgucDMd3OUl+H1xxL89YLPWKuODumdOIBmkWlJlrpGmrKGr/k 1Y/nvy1Th1Lq9HBQ5Whe88sS+LBTXexLiaa5nx/c+N8tP5gc2xB6ScOiU495MhqkVh TW/GcclJJ6Q7FqQGC70ynLm3jvd1kSsQ5A5L0WB/K7hLXSrFZvIjRcK3IgIMAd4NRf wLwYsqwlmwUBe3jSo2lNI5vPcqhM3vs3KGP4oLo5N50BX5baV24ONc16dc+fWR9dK6 t6IUxwt9zpmRA== Message-ID: <15ef4be15016b47e3a77a4ab37f77cec9c49dbae.camel@kernel.org> Subject: Re: performance r nfsd with RWF_DONTCACHE and larger wsizes From: Jeff Layton To: Chuck Lever , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Cc: Mike Snitzer , Trond Myklebust , Jens Axboe , Chris Mason , Anna Schumaker Date: Tue, 06 May 2025 14:30:04 -0400 In-Reply-To: References: <370dd4ae06d44f852342b7ee2b969fc544bd1213.camel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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Layton wrote: > > FYI I decided to try and get some numbers with Mike's RWF_DONTCACHE > > patches for nfsd [1]. Those add a module param that make all reads and > > writes use RWF_DONTCACHE. > >=20 > > 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. > >=20 > > I tested sequential writes using the fio-seq_write.fio test, both with > > and without the module param enabled. > >=20 > > These numbers are from one run each, but they were pretty stable over > > several runs: > >=20 > > # fio /usr/share/doc/fio/examples/fio-seq-write.fio > >=20 > > wsize=3D1M: > >=20 > > Normal: WRITE: bw=3D1034MiB/s (1084MB/s), 1034MiB/s-1034MiB/s (108= 4MB/s-1084MB/s), io=3D910GiB (977GB), run=3D901326-901326msec > > DONTCACHE: WRITE: bw=3D649MiB/s (681MB/s), 649MiB/s-649MiB/s (681MB/s= -681MB/s), io=3D571GiB (613GB), run=3D900001-900001msec > >=20 > > 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. > >=20 > > 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: > >=20 > > wsize=3D4M: > >=20 > > Normal: WRITE: bw=3D1053MiB/s (1104MB/s), 1053MiB/s-1053MiB/s (11= 04MB/s-1104MB/s), io=3D930GiB (999GB), run=3D904526-904526msec > > DONTCACHE: WRITE: bw=3D1191MiB/s (1249MB/s), 1191MiB/s-1191MiB/s (12= 49MB/s-1249MB/s), io=3D1050GiB (1127GB), run=3D902781-902781msec > >=20 > > 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. >=20 > My feeling is that at this point, the NFSD read and write paths are not > currently tuned for large folios -- they break every I/O into single > pages. >=20 *nod* >=20 > > 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? >=20 > Mike has suggested that NFSD should limit the use RWF_UNCACHED to > WRITE requests with large payloads (for some arbitrary definition of > "large"). >=20 Yeah. I think we need something along those lines. >=20 > > This might also be a good reason to think about a larger rsize/wsize > > limit in the client. > >=20 > > 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. >=20 > That's expected for that patch series. >=20 Yep, I figured. > But I have to ask: what problem do you expect RWF_UNCACHED to solve? >=20 I don't have a problem to solve, per-se. I was mainly just wondering what sort of effect RWF_DONTCACHE and larger payloads would have on performance. >=20 > > [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 --=20 Jeff Layton