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 C659186349 for ; Mon, 18 Aug 2025 19:46:07 +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=1755546367; cv=none; b=CzVO42JbTRHXaBFeYMSnUJk1OLbuy7riVsjbf22240klnnFIensgUZLxEYLJS50YOv1aPQM3ck58uz9HhnkaINjeODHzzvnG0h9PGI3JpZURA7ml7hye6mx2EelfxmvZ3yapNNuzRn/CTi+vUobErldmrOBCKmXyEhDas4EWnWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755546367; c=relaxed/simple; bh=GBaRLjIlz5cV0wuWgrtXChqslrHskKFr81BA40vROHw=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=YGdVZK808VK3LbRQzxP64ER5YNZwSJW1Wbt/5dQJuFmnFSxuhp29eLdjtd9IBkSovTe8cH2JTzZs3OfVyAvCmMkzibBtTKsEPtm23DnsMMUP/BhMIVh3ViqieSxrlkvZzLgbM/SJhy3f1igS37bpPVClWXQTxA8uAzFUnA+m5k8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MUCZo6eq; 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="MUCZo6eq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E073C4CEEB; Mon, 18 Aug 2025 19:46:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755546367; bh=GBaRLjIlz5cV0wuWgrtXChqslrHskKFr81BA40vROHw=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=MUCZo6eqYk7d1bx/CbKNbx84zoGwsycKtiQzvoZnIw8eZS21Uap+jBvX2BYE66hut QQbJJS48NHsW91DFCp43VTBW9fQ6xtz+0bhAy5riAV1lEoX3cEMNEboBhxwLU2ERDE YWF8SqBlCWBfNJA5jkKyvpK8EhqT73M8DAm58uOSHNysAylQDXxUAYdrNzRuHi8bPq y1kcxq4Y/q7G0myjLzocRPNRQuYb2jsA5net1QF4O2Q6Bw7KdjFDEN/stt6yqZ8EmC WIttYS9ClWmMi6HntQAGfJrFxlDNStEM1b02fNQhDwmAp0tFx61roBL7w+ZGpE4o6b vFFDyaXIybQRg== Message-ID: Subject: Re: [PATCH v7 6/7] 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: Mon, 18 Aug 2025 15:46:06 -0400 In-Reply-To: <20250815144607.50967-7-snitzer@kernel.org> References: <20250815144607.50967-1-snitzer@kernel.org> <20250815144607.50967-7-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 > Signed-off-by: Mike Snitzer > --- > fs/nfsd/vfs.c | 176 +++++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 168 insertions(+), 8 deletions(-) >=20 > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > index 64732dc8985d6..afcc22fdddefc 100644 > --- a/fs/nfsd/vfs.c > +++ b/fs/nfsd/vfs.c > @@ -1355,6 +1355,169 @@ 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 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; > + > + 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)) > + return false; > + > + memset(write_dio, 0, sizeof(*write_dio)); > + > + 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; > + return true; > + } > + > + 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; > + > + return true; > +} > + > +/* > + * Setup as many as 3 iov_iter based on extents described by @write_dio. > + * @iterp: pointer to pointer to onstack array of 3 iov_iter structs fro= m caller. > + * @iter_is_dio_aligned: pointer to onstack array of 3 bools from 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_dio_iters(struct iov_iter **iterp, bool *iter_is_dio_al= igned, > + struct bio_vec *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) { > + iter_is_dio_aligned[n_iters] =3D false; > + iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt); > + iters[n_iters].count =3D write_dio->start_len; > + ++n_iters; > + } > + > + /* Setup DIO-aligned middle */ > + iter_is_dio_aligned[n_iters] =3D true; > + 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) { > + iter_is_dio_aligned[n_iters] =3D false; > + 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; > +} > + > +static int > +nfsd_issue_write_buffered(struct svc_rqst *rqstp, struct file *file, > + unsigned int nvecs, unsigned long *cnt, > + struct kiocb *kiocb) > +{ > + struct iov_iter iter; > + int host_err; > + > + iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt); > + host_err =3D vfs_iocb_iter_write(file, kiocb, &iter); > + if (host_err < 0) > + return host_err; > + *cnt =3D host_err; > + > + return 0; > +} > + > +static noinline int > +nfsd_issue_write_dio(struct svc_rqst *rqstp, struct svc_fh *fhp, > + struct nfsd_file *nf, loff_t offset, > + unsigned int nvecs, unsigned long *cnt, > + struct kiocb *kiocb) > +{ > + struct nfsd_write_dio write_dio; > + struct file *file =3D nf->nf_file; > + > + if (!nfsd_analyze_write_dio(rqstp, fhp, nf, offset, *cnt, &write_dio)) > + return nfsd_issue_write_buffered(rqstp, file, nvecs, cnt, kiocb); > + else { > + bool iter_is_dio_aligned[3]; > + struct iov_iter iter_stack[3]; > + struct iov_iter *iter =3D iter_stack; > + unsigned int n_iters =3D 0; > + int host_err; > + > + n_iters =3D nfsd_setup_write_dio_iters(&iter, iter_is_dio_aligned, > + rqstp->rq_bvec, nvecs, *cnt, &write_dio); > + *cnt =3D 0; > + for (int i =3D 0; i < n_iters; i++) { > + if (iter_is_dio_aligned[i] && > + nfsd_iov_iter_aligned_bvec(&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) { > + /* Underlying FS will return -EINVAL if misaligned > + * DIO is attempted because it shouldn't be. > + */ > + WARN_ON_ONCE(host_err =3D=3D -EINVAL); > + return host_err; > + } > + *cnt +=3D host_err; > + if (host_err < iter[i].count) /* partial write? */ > + return *cnt; > + } If this ends up doing some buffered I/Os on the unaligned end bits, should we have it issue a vfs_fsync_range() (or maybe use IOCB_SYNC) here as well to ensure that those bits get written back before sending the reply? I worry a bit about an aligned (DIO) read of a page racing in and not seeing data that hasn't been written back yet. > + } > + > + return 0; > +} > + > /** > * nfsd_vfs_write - write data to an already-open file > * @rqstp: RPC execution context > @@ -1382,7 +1545,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_f= h *fhp, > struct super_block *sb =3D file_inode(file)->i_sb; > struct kiocb kiocb; > struct svc_export *exp; > - struct iov_iter iter; > errseq_t since; > __be32 nfserr; > int host_err; > @@ -1419,31 +1581,29 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc= _fh *fhp, > kiocb.ki_flags |=3D IOCB_DSYNC; > =20 > nvecs =3D xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload); > - iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt); > + > since =3D READ_ONCE(file->f_wb_err); > if (verf) > nfsd_copy_write_verifier(verf, nn); > =20 > 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)) > - kiocb.ki_flags |=3D IOCB_DIRECT; > + host_err =3D nfsd_issue_write_dio(rqstp, fhp, nf, offset, > + nvecs, cnt, &kiocb); > break; > case NFSD_IO_DONTCACHE: > kiocb.ki_flags |=3D IOCB_DONTCACHE; > fallthrough; > case NFSD_IO_UNSPECIFIED: > case NFSD_IO_BUFFERED: > + host_err =3D nfsd_issue_write_buffered(rqstp, file, > + nvecs, cnt, &kiocb); > break; > } > - host_err =3D vfs_iocb_iter_write(file, &kiocb, &iter); > if (host_err < 0) { > commit_reset_write_verifier(nn, rqstp, host_err); > goto out_nfserr; > } > - *cnt =3D host_err; > nfsd_stats_io_write_add(nn, exp, *cnt); > fsnotify_modify(file); > host_err =3D filemap_check_wb_err(file->f_mapping, since); --=20 Jeff Layton