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 BD5FB21507C for ; Fri, 21 Feb 2025 15:25:05 +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=1740151505; cv=none; b=r+9n+cJifdnBWxYnUxEzKr+qGSHk+vh5H9tUnqs0TWOzGAiVHGqYM1tTCim9KVgnY+i/fO9LQCxip7CvaxDpPgurPcefQlcaVaSjba9gbV7f1GaWNjiOtlXQBhmN7R2F3HaC/a/ZDfcncwqCTTT+Ceqgri0aDgKe+cPrvouJtmY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740151505; c=relaxed/simple; bh=w77L+NuRdSfQ7Od4SEPxhGQNOyziiMa9SBESSwG6wfw=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=b0P3waUvn3e6tUTs7JcN+tZvC/1gHxZ7EYoJh3ablJJA5qMgV/xOrKzpRu3B0cc13MU4b5ygKNaO4/8M1sUQ26Z8DYRKbs8Mu81u2YQF7RRs1XivCpu22XHrDulM/jt+Mtg+zUkYVsk/3COK97p5ShuDK8N6ydI1IFHBiyJ0+Cg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SaoMHp5u; 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="SaoMHp5u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 694ABC4AF10; Fri, 21 Feb 2025 15:25:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740151505; bh=w77L+NuRdSfQ7Od4SEPxhGQNOyziiMa9SBESSwG6wfw=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=SaoMHp5uIPZOx4PQwMrTLYupkt7hl82JFyN8zuNAd8YInFIYZRJzuLWTSzioASywp M35/CLqLB/EkudRXOaEyoj/nHVllhGnEuHbuH6GkPbxBO8LNKlezA7hIzoXOX3JjPa f0oiUJ0tlmEB4u4SwXPAf6WaszJUaOvclN+YK/YuAy+5GA5Of53YpYs7+VUu50yluM auQ1fkWxPMGen5WEcAM3rYWLBbe/QPRk22sM0eHkZGnI1Zzz4SBMayRM4lOc0HF71E HzAyf4mdu6oVJEjw1UvmhDjxCYI06aU2NF7wp0zfYmj9SLzZ7Z1t1ZCSCzlwWWmXQT ZcYwJxmkqnNqw== Message-ID: Subject: Re: nfsd: add the ability to enable use of RWF_DONTCACHE for all nfsd IO From: Jeff Layton To: Mike Snitzer , Chuck Lever Cc: linux-nfs@vger.kernel.org, Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey , axboe@kernel.dk Date: Fri, 21 Feb 2025 10:25:03 -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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On 2/20/25 12:12 PM, Mike Snitzer wrote: > > > Add nfsd 'nfsd_dontcache' modparam so that "Any data read or written > > > 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, does > > it make sense to make it a separate control for READ and one for WRITE? > > 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 in > time for LSF. >=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. > > However, to add any such administrative control, I'd like to see some > > performance numbers. I think we need to enumerate the cases (I/O types) > > that are most interesting to examine: small memory NFS servers; lots of > > small unaligned I/O; server-side CPU per byte; storage interrupt rates; > > any others? > >=20 > > And let's see some user/admin documentation (eg when should this settin= g > > 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 setting > > for this mechanism for a long time, or do we expect that the setting ca= n > > become automatic/uninteresting after a period of experimentation? > >=20 > > * It might be argued that putting these experimental tunables under /sy= s > > eliminates the support longevity question, since there aren't strict > > rules about removing files under /sys. Isn't /sys covered by the same ABI guarantees? I know debugfs isn't, but I'm not sure about /sys. >=20 > Right, I do think a sysfs knob (that defaults to disabled, requires > user opt-in) is a pretty useful and benign means to expose > experimental functionality. >=20 > And I agree with all you said needed above, I haven't had the time to > focus on DONTCACHE since ~Decemeber, I just picked up my old patches > from that time and decided to send the NFSD one since DONTCACHE has > been merged for 6.14. >=20 > > =20 > > > FOP_DONTCACHE must be advertised as supported by the underlying > > > filesystem (e.g. XFS), otherwise if/when 'nfsd_dontcache' is enabled > > > all IO will fail with -EOPNOTSUPP. > >=20 > > It would be better all around if NFSD simply ignored the setting in the > > cases where the underlying file system doesn't implement DONTCACHE. >=20 > I'll work on making it so. >=20 > >=20 > >=20 > > > Signed-off-by: Mike Snitzer > > > --- > > > fs/nfsd/vfs.c | 17 ++++++++++++++++- > > > 1 file changed, 16 insertions(+), 1 deletion(-) > > >=20 > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > > index 29cb7b812d71..d7e49004e93d 100644 > > > --- a/fs/nfsd/vfs.c > > > +++ b/fs/nfsd/vfs.c > > > @@ -955,6 +955,11 @@ nfsd_open_verified(struct svc_fh *fhp, int may_f= lags, struct file **filp) > > > return __nfsd_open(fhp, S_IFREG, may_flags, filp); > > > } > > > =20 > > > +static bool nfsd_dontcache __read_mostly =3D false; > > > +module_param(nfsd_dontcache, bool, 0644); > > > +MODULE_PARM_DESC(nfsd_dontcache, > > > + "Any data read or written by nfsd will be removed from the page c= ache upon completion."); > > > + > > > /* > > > * Grab and keep cached pages associated with a file in the svc_rqst > > > * so that they can be passed to the network sendmsg routines > > > @@ -1084,6 +1089,7 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, s= truct svc_fh *fhp, > > > loff_t ppos =3D offset; > > > struct page *page; > > > ssize_t host_err; > > > + rwf_t flags =3D 0; > > > =20 > > > v =3D 0; > > > total =3D *count; > > > @@ -1097,9 +1103,12 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, = struct svc_fh *fhp, > > > } > > > WARN_ON_ONCE(v > ARRAY_SIZE(rqstp->rq_vec)); > > > =20 > > > + if (nfsd_dontcache) > > > + flags |=3D RWF_DONTCACHE; > > > + > > > trace_nfsd_read_vector(rqstp, fhp, offset, *count); > > > iov_iter_kvec(&iter, ITER_DEST, rqstp->rq_vec, v, *count); > > > - host_err =3D vfs_iter_read(file, &iter, &ppos, 0); > > > + host_err =3D vfs_iter_read(file, &iter, &ppos, flags); > > > return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_= err); > > > } > > > =20 > > > @@ -1186,6 +1195,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct s= vc_fh *fhp, struct nfsd_file *nf, > > > if (stable && !fhp->fh_use_wgather) > > > flags |=3D RWF_SYNC; > > > =20 > > > + if (nfsd_dontcache) > > > + flags |=3D RWF_DONTCACHE; > > > + > > > iov_iter_kvec(&iter, ITER_SOURCE, vec, vlen, *cnt); > > > since =3D READ_ONCE(file->f_wb_err); > > > if (verf) > > > @@ -1237,6 +1249,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct s= vc_fh *fhp, struct nfsd_file *nf, > > > */ > > > bool nfsd_read_splice_ok(struct svc_rqst *rqstp) > > > { > > > + if (nfsd_dontcache) /* force the use of vfs_iter_read for reads */ > > > + return false; > > > + > >=20 > > Urgh. >=20 > Heh, yeah, bypassing splice was needed given dontcache hooks off vfs_iter= _read. >=20 > > So I've been mulling over simply removing the splice read path. > >=20 > > - Less code, less complexity, smaller test matrix > >=20 > > - How much of a performance loss would result? > >=20 > > - Would such a change make it easier to pass whole folios from > > the file system directly to the network layer? >=20 > Good to know. >=20 --=20 Jeff Layton