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smtp.kernel.org (Postfix) with ESMTPSA id 514D0C4CEFC; Tue, 15 Jul 2025 11:57:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1752580659; bh=gI8v3SsRYspM6Pl3TWlr02a3n5x5jLVnyYIUCMpkwx4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=NSzuHI3aX99zLfUnrb6hmeg//9CgweQRV5WEk3JGGa2soU5Ahc1rFtc4YBHRferAN T9Mh4UPqIQFjJ+Qqtf2OkhAuR3tBQpvIOM9IVzdQv4qKrfa7o2xL9r/xxlufkFoTiS DE6TP3XAtq6gOdKEgQ4uCxNxhl2siD2L4qZEFDK4ZoE6FwIQqXVDZPC9K9mxhi9LKM 5e4cRyEU2yZuSN7g/7rbnk3Jr0c6EAlqK5n0ExVUwauqKCFVkqWUDDXu8YSbFwRF3K vfkZEesW9KcL8uq8BlWd+XPdUxf/QWutTMFAFziJvfTxZ0Yia8EqTWrJX08+M3kNXZ o18lyVyo+dFjg== Message-ID: <44afdba79f4ea9f6424840b236bc2d61ea51ad33.camel@kernel.org> Subject: Re: [RFC PATCH v2 6/8] NFSD: add io_cache_read controls to debugfs interface From: Jeff Layton To: Mike Snitzer , Chuck Lever Cc: NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Trond Myklebust , Anna Schumaker , linux-nfs@vger.kernel.org, linus-fsdevel@vger.kernel.org, linux-mm@kvack.org Date: Tue, 15 Jul 2025 07:57:37 -0400 In-Reply-To: References: <20250708160619.64800-1-snitzer@kernel.org> <20250708160619.64800-7-snitzer@kernel.org> <6a05d14f-dbf6-4786-ba08-c57f8f4c64e6@oracle.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf 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 Ln/ePlNZ 7FcQmFZGtSy5Eu+R4Q3LtpLMp1ilAV6CIdpkgplEmqeIXdu9H6mvljdQqjzeGYsKPy7Ck3z2oIcZDHWHzuuyrQw/tXinXsz/pbLNZAXbXD7xw/iYdoD3Sci8kh2mIn1hz6xmjGaQ81QEs0q1WcFCyEo4qjHIo/M+sEWSBVYQtjMe0lG+xxVDuF+TVr7CVkmdqU2Gqo8e5w00MFhk+wms8pSiqfv/hSp9tF1d/HsluZJBXqq1zEt5A0B2Z3tRiyMPJXbkFtU2qPj2tn+cJTmgZRwzpsoqKsNq0DL8n X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2025-07-14 at 12:47 -0400, Mike Snitzer wrote: > On Thu, Jul 10, 2025 at 06:46:37PM -0400, Chuck Lever wrote: > > On 7/10/25 10:06 AM, Jeff Layton wrote: > > > On Tue, 2025-07-08 at 12:06 -0400, Mike Snitzer wrote: > > > > Add 'io_cache_read' to NFSD's debugfs interface so that: Any data > > > > read by NFSD will either be: > > > > - cached using page cache (NFSD_IO_BUFFERED=3D0) > > > > - cached but removed from the page cache upon completion > > > > (NFSD_IO_DONTCACHE=3D1). > > > > - not cached (NFSD_IO_DIRECT=3D2) > > > >=20 > > > > io_cache_read is 0 by default. It may be set by writing to: > > > > /sys/kernel/debug/nfsd/io_cache_read > > > >=20 > > > > If NFSD_IO_DONTCACHE is specified using 1, FOP_DONTCACHE must be > > > > advertised as supported by the underlying filesystem (e.g. XFS), > > > > otherwise all IO flagged with RWF_DONTCACHE will fail with > > > > -EOPNOTSUPP. > > > >=20 > > > > If NFSD_IO_DIRECT is specified using 2, the IO must be aligned > > > > relative to the underlying block device's logical_block_size. Also = the > > > > memory buffer used to store the read must be aligned relative to th= e > > > > underlying block device's dma_alignment. > > > >=20 > > > > Signed-off-by: Mike Snitzer > > > > --- > > > > fs/nfsd/debugfs.c | 53 +++++++++++++++++++++++++++++++++++++++++++= ++++ > > > > fs/nfsd/nfsd.h | 8 +++++++ > > > > fs/nfsd/vfs.c | 15 ++++++++++++++ > > > > 3 files changed, 76 insertions(+) > > > >=20 > > > > diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c > > > > index 84b0c8b559dc..709646af797a 100644 > > > > --- a/fs/nfsd/debugfs.c > > > > +++ b/fs/nfsd/debugfs.c > > > > @@ -27,11 +27,61 @@ static int nfsd_dsr_get(void *data, u64 *val) > > > > static int nfsd_dsr_set(void *data, u64 val) > > > > { > > > > nfsd_disable_splice_read =3D (val > 0) ? true : false; > > > > + if (!nfsd_disable_splice_read) { > > > > + /* > > > > + * Cannot use NFSD_IO_DONTCACHE or NFSD_IO_DIRECT > > > > + * if splice_read is enabled. > > > > + */ > > > > + nfsd_io_cache_read =3D NFSD_IO_BUFFERED; > > > > + } > > > > return 0; > > > > } > > > > =20 > > > > DEFINE_DEBUGFS_ATTRIBUTE(nfsd_dsr_fops, nfsd_dsr_get, nfsd_dsr_set= , "%llu\n"); > > > > =20 > > > > +/* > > > > + * /sys/kernel/debug/nfsd/io_cache_read > > > > + * > > > > + * Contents: > > > > + * %0: NFS READ will use buffered IO (default) > > > > + * %1: NFS READ will use dontcache (buffered IO w/ dropbehind) > > > > + * %2: NFS READ will use direct IO > > > > + * > > > > + * The default value of this setting is zero (buffered IO is > > > > + * used). This setting takes immediate effect for all NFS > > > > + * versions, all exports, and in all NFSD net namespaces. > > > > + */ > > > > + > > >=20 > > > Could we switch this to use a string instead? Maybe > > > buffered/dontcache/direct ? > >=20 > > That thought occurred to me too, since it would make the API a little > > more self-documenting, and might be a harbinger of what a future > > export option might look like. > >=20 > >=20 > > > > +static int nfsd_io_cache_read_get(void *data, u64 *val) > > > > +{ > > > > + *val =3D nfsd_io_cache_read; > > > > + return 0; > > > > +} > > > > + > > > > +static int nfsd_io_cache_read_set(void *data, u64 val) > > > > +{ > > > > + switch (val) { > > > > + case NFSD_IO_DONTCACHE: > > > > + case NFSD_IO_DIRECT: > > > > + /* > > > > + * Must disable splice_read when enabling > > > > + * NFSD_IO_DONTCACHE or NFSD_IO_DIRECT. > > > > + */ > > > > + nfsd_disable_splice_read =3D true; > > > > + nfsd_io_cache_read =3D val; > > > > + break; > > > > + case NFSD_IO_BUFFERED: > > > > + default: > > > > + nfsd_io_cache_read =3D NFSD_IO_BUFFERED; > > > > + break; > > >=20 > > > I think the default case should leave nfsd_io_cache_read alone and > > > return an error. If we add new values later, and someone tries to use > > > them on an old kernel, it's better to make that attempt error out. > > >=20 > > > Ditto for the write side controls. > >=20 > > +1 on both accounts. >=20 > I started to implement this just now (so that I can kick v3 of this > patchset out of the nest today) but soon found that debugfs doesn't > provide string-based interface controls. >=20 > See simple_attr_open() (which is used by DEFINE_DEBUGFS_ATTRIBUTE). > It only allows u64 to be set/get. >=20 > I'll fix the default case to return an error for now though. >=20 > Once we graduate from debugfs to a proper per-export control we can > impose string controls/mapping, e.g.: >=20 > +static u64 nfsd_io_cache_string_to_mode(const char *nfsd_io_cache_string= ) > +{ > + u64 val =3D NFSD_IO_UNKNOWN; > + > + if (!strncmp(nfsd_io_cache_string, NFSD_IO_BUFFERED_string, > + strlen(NFSD_IO_BUFFERED_string))) > + val =3D NFSD_IO_BUFFERED; > + else if (!strncmp(nfsd_io_cache_string, NFSD_IO_DONTCACHE_string, > + strlen(NFSD_IO_DONTCACHE_string))) > + val =3D NFSD_IO_DONTCACHE; > + else if (!strncmp(nfsd_io_cache_string, NFSD_IO_DIRECT_string, > + strlen(NFSD_IO_DIRECT_string))) > + val =3D NFSD_IO_DIRECT; > + > + return val; > +} > + > +static const char * > +nfsd_io_cache_mode_to_string(const char *nfsd_io_cache_string) > +{ > + char *nfsd_io_cache_string; > + > + switch (val) { > + case NFSD_IO_BUFFERED: > + nfsd_io_cache_string =3D NFSD_IO_BUFFERED_string; > + break; > + case NFSD_IO_DONTCACHE: > + nfsd_io_cache_string =3D NFSD_IO_DONTCACHE_string; > + break; > + case NFSD_IO_DIRECT: > + nfsd_io_cache_string =3D NFSD_IO_DIRECT_string; > + break; > + case NFSD_IO_UNKNOWN: > + nfsd_io_cache_string =3D NFSD_IO_UNKNOWN_string; > + break; > + } > + > + return nfsd_io_cache_string; > +} Bummer. I guess we could just roll our own using the seqfile interfaces and put it in the same directory. I may take a stab at that before we ship this. For now, we can stick with the integers. Thanks for fixing up the default case! --=20 Jeff Layton