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 714C31A23B7 for ; Fri, 21 Feb 2025 15:42:21 +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=1740152541; cv=none; b=SWBpXZGI5sPe0iBRG/fvOXfCuu4L56xaVP48bPupaDyacGpDwpJQ9LRrlMwmRZngh6GRmKBF6QxPA6899iFeC51auT5lW8QChT2jTZrRlD9gwKvFzikGe4hYzaULBUfOzK8DWiCq8mZVFDM3P7e0PBLkBARAUDQoTKv2Zv0TJFE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740152541; c=relaxed/simple; bh=YziY3Yf0AVna8mtsiV1EFfFKd1PEbsd0LECb/dp78As=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=FHon2fuWbUDYS3jNsquGFdb0sv6oU3T8epy88zNigxeosWntFjDKaHpQXTif24kjzbh0JoQfuiXBvzAUIaJqNhT5q/q3xkb37zOk6W8xKED5I3lrIYKkUqYYvv8YdyQjT9S9XMHVhQfVk8ethcreaz7ojIngrn28R5c1Ac8aeGM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IWbgpCHx; 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="IWbgpCHx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35502C4CED6; Fri, 21 Feb 2025 15:42:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740152540; bh=YziY3Yf0AVna8mtsiV1EFfFKd1PEbsd0LECb/dp78As=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=IWbgpCHxPzYuouNatO31SH7xrO0eNoIUrIc8Fzp3rD/HHjd0YIFwng1GbJuPxPBtt XnzhbxEPPBE/a8HJSRvmvS4fiFfNvMulNB2XWkVh1+DN9IuFHIC9BA37S8HB7bX1Hv gFQEmstfWv5jnsnO0x9VFWQkU9VdPL7yiWUQf9+ynDBDpXWgbCeaT/Mc5a9Q066lia GxdJl2zaQ2puTQUvvvdU4sKSTApvqURjMgCRLSxhz7fmEcVrRHgV+ebbmFINWvW1xN zgA7Z6ODxWW4CmFVHhe4z2oBiuVZMU5ZCI/QUsfdusb5qA/FuKIOj6H3GwuuHmihim WP/n5phPkvn+g== Message-ID: Subject: Re: nfsd: add the ability to enable use of RWF_DONTCACHE for all nfsd IO From: Jeff Layton To: Mike Snitzer Cc: Chuck Lever , linux-nfs@vger.kernel.org, Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey , axboe@kernel.dk Date: Fri, 21 Feb 2025 10:42:19 -0500 In-Reply-To: References: <20250220171205.12092-1-snitzer@kernel.org> 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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Snitzer wrote: > > > On Thu, Feb 20, 2025 at 01:17:42PM -0500, Chuck Lever wrote: > > > > [ Adding NFSD reviewers ... ] > > > >=20 > > > > On 2/20/25 12:12 PM, Mike Snitzer wrote: > > > > > Add nfsd 'nfsd_dontcache' modparam so that "Any data read or writ= ten > > > > > by nfsd will be removed from the page cache upon completion." > > > > >=20 > > > > > nfsd_dontcache is disabled by default. It may be enabled with: > > > > > echo Y > /sys/module/nfsd/parameters/nfsd_dontcache > > > >=20 > > > > A per-export setting like an export option would be nicer. Also, do= es > > > > it make sense to make it a separate control for READ and one for WR= ITE? > > > > My trick knee suggests caching read results is still going to add > > > > significant value, but write, not so much. > > >=20 > > > My intent was to make 6.14's DONTCACHE feature able to be tested in > > > the context of nfsd in a no-frills way. I realize adding the > > > nfsd_dontcache knob skews toward too raw, lacks polish. But I'm > > > inclined to expose such course-grained opt-in knobs to encourage > > > others' discovery (and answers to some of the questions you pose > > > below). I also hope to enlist all NFSD reviewers' help in > > > categorizing/documenting where DONTCACHE helps/hurts. ;) > > >=20 > > > And I agree that ultimately per-export control is needed. I'll take > > > the time to implement that, hopeful to have something more suitable i= n > > > time for LSF. > > >=20 > >=20 > > Would it make more sense to hook DONTCACHE up to the IO_ADVISE > > operation in RFC7862? IO_ADVISE4_NOREUSE sounds like it has similar > > meaning? That would give the clients a way to do this on a per-open > > basis. >=20 > Just thinking aloud here but: Using a DONTCACHE scalpel on a per open > basis quite likely wouldn't provide the required page reclaim relief > if the server is being hammered with normal buffered IO. Sure that > particular DONTCACHE IO wouldn't contribute to the problem but it > would still be impacted by those not opting to use DONTCACHE on entry > to the server due to needing pages for its DONTCACHE buffered IO. >=20 Actually, now that I read the spec, it looks like you could just embed an IO_ADVISE operation in the read compound: PUTFH + IO_ADVISE(for the range that you're reading) + READ() operation That said, that does nothing for v3 reads, which I imagine you're interested in hooking up here too. > > > > However, to add any such administrative control, I'd like to see so= me > > > > performance numbers. I think we need to enumerate the cases (I/O ty= pes) > > > > that are most interesting to examine: small memory NFS servers; lot= s of > > > > small unaligned I/O; server-side CPU per byte; storage interrupt ra= tes; > > > > any others? > > > >=20 > > > > And let's see some user/admin documentation (eg when should this se= tting > > > > be enabled? when would it be contra-indicated?) > > > >=20 > > > > The same arguments that applied to Cedric's request to make maximum= RPC > > > > size a tunable setting apply here. Do we want to carry a manual set= ting > > > > for this mechanism for a long time, or do we expect that the settin= g can > > > > become automatic/uninteresting after a period of experimentation? > > > >=20 > > > > * It might be argued that putting these experimental tunables under= /sys > > > > eliminates the support longevity question, since there aren't str= ict > > > > rules about removing files under /sys. > >=20 > > Isn't /sys covered by the same ABI guarantees? I know debugfs isn't, > > but I'm not sure about /sys. >=20 > Only if you add them to the ABI docs as supported (at least that is my > experience relative to various block limits knobs, etc). But yeah, > invariably that invites a cat and mouse game of users using the knob > and then complaining loudly if/when it goes away. >=20 > Mike --=20 Jeff Layton