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 028DD35977 for ; Thu, 31 Jul 2025 20:53:43 +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=1753995225; cv=none; b=U+VvxukfMTqFBlSPvH0MIHmUu0sY2VbjyHeyNRNAdkwktC0XMD09jfkNErYnk2O0mLBR/1wNGD6io+xbzzzG/pq2UAAoR9IUtMgMu/V+xx4eMp5CZrkhE+X9ZmOwPDFxoSQD1YxuL96ERtgN7vyu7qIbJzEN/fQqGLXfXjQKGhs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753995225; c=relaxed/simple; bh=uyIh5MvZ2bbPsQUMuUGVhMut8PPUGORRPGjzQAJr0ks=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=fLe/1rKUg7AZ/ev1O4gogBGs9jHYL7npiCiHMpJsKKbJ7366McRI/FoHyu8rr9CW1jGjxJ6DF63eh/IUiGSkq3xvEeD+z2J3J+ambQjqC5VpykoFPhCXfJqiscVkbPFretVjdHZiHUWgz5HM57xHoiQlLWib8oI0f6nPIqaMLPU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oKm6hjQY; 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="oKm6hjQY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3CFABC4CEEF; Thu, 31 Jul 2025 20:53:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753995223; bh=uyIh5MvZ2bbPsQUMuUGVhMut8PPUGORRPGjzQAJr0ks=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=oKm6hjQYcQqGITL/kTvDH0W2zKE9v53al4tinBQ/b9EVstB6LaX7qIwgVmh/Ey01/ wr1xdFGtTiJW8Ipi4yxIoxYo+68EiAFf531wfk9c8rFgSwpCecw14HJw8WUgqOKjKn wGQ27o4emsClD0njqnHl5REglVP9NpVEplAg6BXwu90hnMZaOqPQ/iD5Jzz0bVJWDM sQQhvowVi++LakK+GfN3PjiXsJF7JkO6+EaCWOd2yVU37zUuVvsPxJdIDhjYhxxPFu 1FKFKe8bsoo2qseWmVwZ8mH3w0rjsN6VGheo9GsfyEFr/+UyCxzmUBBwc2mtb9mT6h 83KsKgdpu5umA== Message-ID: Subject: Re: [PATCH v2 3/4] NFSD: issue WRITEs using O_DIRECT even if IO is misaligned From: Jeff Layton To: Mike Snitzer , Chuck Lever Cc: linux-nfs@vger.kernel.org Date: Thu, 31 Jul 2025 16:53:42 -0400 In-Reply-To: <20250731194448.88816-4-snitzer@kernel.org> References: <20250731194448.88816-1-snitzer@kernel.org> <20250731194448.88816-4-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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The large middle extent is DIO-aligned and > the start and/or end are misaligned. Buffered IO is used for the > misaligned extents and O_DIRECT is used for the middle DIO-aligned > extent. >=20 > The nfsd_analyze_write_dio trace event shows how NFSD splits a given > misaligned WRITE into a mix of misaligned extent(s) and a DIO-aligned > extent. >=20 > This combination of trace events is useful: >=20 > echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_opened/enable > echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_analyze_write_dio/enable > echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_io_done/enable > echo 1 > /sys/kernel/tracing/events/xfs/xfs_file_direct_write/enable >=20 > Which for this dd command: >=20 > dd if=3D/dev/zero of=3D/mnt/share1/test bs=3D47008 count=3D2 oflag=3Ddi= rect >=20 > Results in: >=20 > nfsd-55714 [043] ..... 79976.260851: nfsd_write_opened: xid=3D0x966c5= d2d fh_hash=3D0x4d34e6c1 offset=3D0 len=3D47008 > nfsd-55714 [043] ..... 79976.260852: nfsd_analyze_write_dio: xid=3D0x= 966c5d2d fh_hash=3D0x4d34e6c1 offset=3D0 len=3D47008 start=3D0+0 middle=3D0= +45056 end=3D45056+1952 > nfsd-55714 [043] ..... 79976.260857: xfs_file_direct_write: dev 259:1= 2 ino 0x3e00008f disize 0x0 pos 0x0 bytecount 0xb000 > nfsd-55714 [043] ..... 79976.260965: nfsd_write_io_done: xid=3D0x966c= 5d2d fh_hash=3D0x4d34e6c1 offset=3D0 len=3D47008 >=20 > nfsd-55714 [043] ..... 79976.307762: nfsd_write_opened: xid=3D0x67e5c= e6f fh_hash=3D0x4d34e6c1 offset=3D47008 len=3D47008 > nfsd-55714 [043] ..... 79976.307762: nfsd_analyze_write_dio: xid=3D0x= 67e5ce6f fh_hash=3D0x4d34e6c1 offset=3D47008 len=3D47008 start=3D47008+2144= middle=3D49152+40960 end=3D90112+3904 > nfsd-55714 [043] ..... 79976.307797: xfs_file_direct_write: dev 259:1= 2 ino 0x3e00008f disize 0xc000 pos 0xc000 bytecount 0xa000 > nfsd-55714 [043] ..... 79976.307866: nfsd_write_io_done: xid=3D0x67e5= ce6f fh_hash=3D0x4d34e6c1 offset=3D47008 len=3D47008 >=20 > Signed-off-by: Mike Snitzer > --- > fs/nfsd/vfs.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 124 insertions(+), 11 deletions(-) >=20 > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > index e4855c32dad12..23360825455a2 100644 > --- a/fs/nfsd/vfs.c > +++ b/fs/nfsd/vfs.c > @@ -1314,6 +1314,113 @@ static int wait_for_concurrent_writes(struct file= *file) > return err; > } > =20 > +struct nfsd_write_dio > +{ > + loff_t middle_offset; /* Offset for start of DIO-aligned middle */ > + loff_t end_offset; /* Offset for start of DIO-aligned end */ > + ssize_t start_len; /* Length for misaligned first extent */ > + ssize_t middle_len; /* Length for DIO-aligned middle extent */ > + ssize_t end_len; /* Length for misaligned last extent */ > +}; > + > +static void init_nfsd_write_dio(struct nfsd_write_dio *write_dio) > +{ > + memset(write_dio, 0, sizeof(*write_dio)); > +} > + > +static bool nfsd_analyze_write_dio(struct svc_rqst *rqstp, struct svc_fh= *fhp, > + struct nfsd_file *nf, loff_t offset, > + unsigned long len, struct nfsd_write_dio *write_dio) > +{ > + const u32 dio_blocksize =3D nf->nf_dio_offset_align; > + loff_t orig_end, middle_end, start_end, start_offset =3D offset; > + ssize_t start_len =3D len; > + bool aligned =3D true; > + > + if (WARN_ONCE(!nf->nf_dio_mem_align || !dio_blocksize, > + "%s: underlying filesystem has not provided DIO alignment info\n= ", > + __func__)) > + return false; > + > + if (WARN_ONCE(dio_blocksize > PAGE_SIZE, > + "%s: underlying storage's dio_blocksize=3D%u > PAGE_SIZE=3D%lu\n= ", > + __func__, dio_blocksize, PAGE_SIZE)) > + return false; > + > + if (unlikely(len < dio_blocksize)) { > + aligned =3D false; > + goto out; > + } > + > + if (((offset | len) & (dio_blocksize-1)) =3D=3D 0) { > + /* already DIO-aligned, no misaligned head or tail */ > + write_dio->middle_offset =3D offset; > + write_dio->middle_len =3D len; > + /* clear these for the benefit of trace_nfsd_analyze_write_dio */ > + start_offset =3D 0; > + start_len =3D 0; > + goto out; > + } > + > + start_end =3D round_up(offset, dio_blocksize); > + start_len =3D start_end - offset; > + orig_end =3D offset + len; > + middle_end =3D round_down(orig_end, dio_blocksize); > + > + write_dio->start_len =3D start_len; > + write_dio->middle_offset =3D start_end; > + write_dio->middle_len =3D middle_end - start_end; > + write_dio->end_offset =3D middle_end; > + write_dio->end_len =3D orig_end - middle_end; > +out: > + trace_nfsd_analyze_write_dio(rqstp, fhp, offset, len, start_offset, sta= rt_len, > + write_dio->middle_offset, write_dio->middle_len, > + write_dio->end_offset, write_dio->end_len); > + return aligned; > +} > + > +/* > + * Setup as many as 3 iov_iter based on extents possibly described by @w= rite_dio. > + * @iterp: pointer to pointer to onstack array of 3 iov_iter structs fro= m caller. > + * @rq_bvec: backing bio_vec used to setup all 3 iov_iter permutations. > + * @nvecs: number of segments in @rq_bvec > + * @cnt: size of the request in bytes > + * @write_dio: nfsd_write_dio struct that describes start, middle and en= d extents. > + * > + * Returns the number of iov_iter that were setup. > + */ > +static int nfsd_setup_write_iters(struct iov_iter **iterp, struct bio_ve= c *rq_bvec, > + unsigned int nvecs, unsigned long cnt, > + struct nfsd_write_dio *write_dio) > +{ > + int n_iters =3D 0; > + struct iov_iter *iters =3D *iterp; > + > + /* Setup misaligned start? */ > + if (write_dio->start_len) { > + iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt); > + iters[n_iters].count =3D write_dio->start_len; > + n_iters++; > + } > + > + /* Setup possibly DIO-aligned middle */ > + iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt); > + if (write_dio->start_len) > + iov_iter_advance(&iters[n_iters], write_dio->start_len); > + iters[n_iters].count -=3D write_dio->end_len; > + n_iters++; > + > + /* Setup misaligned end? */ > + if (write_dio->end_len) { > + iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt); > + iov_iter_advance(&iters[n_iters], > + write_dio->start_len + write_dio->middle_len); > + n_iters++; > + } > + > + return n_iters; > +} > + > /** > * nfsd_vfs_write - write data to an already-open file > * @rqstp: RPC execution context > @@ -1348,9 +1455,11 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_= fh *fhp, > unsigned int pflags =3D current->flags; > bool restore_flags =3D false; > unsigned int nvecs; > - struct iov_iter iter_stack[1]; > + struct iov_iter iter_stack[3]; > struct iov_iter *iter =3D iter_stack; > unsigned int n_iters =3D 0; > + bool dio_aligned =3D false; > + struct nfsd_write_dio write_dio; > =20 > trace_nfsd_write_opened(rqstp, fhp, offset, *cnt); > =20 > @@ -1379,18 +1488,12 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc= _fh *fhp, > if (stable && !fhp->fh_use_wgather) > kiocb.ki_flags |=3D IOCB_DSYNC; > =20 > - nvecs =3D xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload); > - iov_iter_bvec(&iter[0], ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt); > - n_iters++; > - > + init_nfsd_write_dio(&write_dio); > switch (nfsd_io_cache_write) { > case NFSD_IO_DIRECT: > - /* direct I/O must be aligned to device logical sector size */ > - if (nf->nf_dio_mem_align && nf->nf_dio_offset_align && > - (((offset | *cnt) & (nf->nf_dio_offset_align-1)) =3D=3D 0) && > - iov_iter_is_aligned(&iter[0], nf->nf_dio_mem_align - 1, > - nf->nf_dio_offset_align - 1)) > - kiocb.ki_flags =3D IOCB_DIRECT; > + if (nfsd_analyze_write_dio(rqstp, fhp, nf, offset, > + *cnt, &write_dio)) > + dio_aligned =3D true; > break; > case NFSD_IO_DONTCACHE: > kiocb.ki_flags =3D IOCB_DONTCACHE; > @@ -1399,12 +1502,22 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc= _fh *fhp, > break; > } > =20 > + nvecs =3D xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload); > + n_iters =3D nfsd_setup_write_iters(&iter, rqstp->rq_bvec, nvecs, *cnt, = &write_dio); > + > *cnt =3D 0; > for (int i =3D 0; i < n_iters; i++) { > since =3D READ_ONCE(file->f_wb_err); > if (verf) > nfsd_copy_write_verifier(verf, nn); > =20 > + if (dio_aligned) { > + if (iov_iter_is_aligned(&iter[i], nf->nf_dio_mem_align - 1, > + nf->nf_dio_offset_align - 1)) > + kiocb.ki_flags |=3D IOCB_DIRECT; > + else > + kiocb.ki_flags &=3D ~IOCB_DIRECT; > + } > host_err =3D vfs_iocb_iter_write(file, &kiocb, &iter[i]); > if (host_err < 0) { > commit_reset_write_verifier(nn, rqstp, host_err); Reviewed-by: Jeff Layton