From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 B68944A441F for ; Thu, 15 Oct 2026 23:33:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792107199; cv=none; b=NYLSpSizxvtcOmjhJLck7Ig5oN7He4YkL9bWpgRKG2YikBG98r02F8zfedLy7oLNycMe4zJCPq3MiXLTb2p2sB21LFN69mEos213Xpm04TUXZLDDDGkLD6Ct3VHKNz8zGm63wLkTYebktAFwxJZoTHfTiN98gsYJQbgKsv2oZTo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792107199; c=relaxed/simple; bh=QqBUav8oXeue5ROG8hZcMqVSL4lem2lZepOpScjxtOo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=AeNd0tPq0vastx4w3kxxfKrCdUAjyxJgbF4KvVsCoEQW1ZA9SY8Bf50ld9GC2cKn00Y/OGpUP0Jg1gpP+Qpn69PEPQPAsqJhTJbYDOMcsZ0k9+jwyW2NupWrWgZwlYuiJu1rtnq1qs/VWaZ02U+jQAo7FRnc4zdb/pTWINfGRXg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mfPATXj0; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mfPATXj0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2DD9B1F000C4; Thu, 15 Oct 2026 23:33:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792107198; bh=GBemQGCyU69s/WwVOcpeFu3LvfmHsaYEii5qBAWj8sU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=mfPATXj0eeL7I/tBnomc8jXLBJvcptUsUIIYEFBrrlRLnm4cvc3GaA2dbhlVLw3qL dEijXgXG8BD4+HA8/PAMwN4hhY7gzJQDkiTqay9tCJV6MWYSn4V0f2LdHrZj4CzHZc f3F6cmfNIPgyVlqoMeUk77YI/V+xuyrbdteztkeKJ2pU1cJ0xoXYTRzyx6MCLb/4lS HQ9eiMzmnITZlfJOLi9FrFQRV8mut60fZzLLONV8Gcel2gBPYG7GMiPchDk30Zjw1u OxZBpnYqSmEhuSydt+VBWsTQcVJUCydlaBbeQnnax0DzOsHxjMK+u7IKCOZfHkCtRi CeiNr35uGOLgQ== From: Mike Snitzer To: Chuck Lever , Jeff Layton Cc: linux-nfs@vger.kernel.org, NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Christoph Hellwig , Jens Axboe , Matthew Wilcox , linux-mm@kvack.org Subject: [PATCH v4 06/10] NFSD: persist a synchronous direct-mode WRITE once, after all of its segments Date: Thu, 15 Oct 2026 19:33:05 -0400 Message-ID: <20261015233309.42999-7-snitzer@kernel.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20261015233309.42999-1-snitzer@kernel.org> References: <20261015233309.42999-1-snitzer@kernel.org> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nfsd_direct_write() may issue a WRITE as up to three segments: a buffered prefix, a direct middle and a buffered suffix. For a FILE_SYNC or DATA_SYNC WRITE the kiocb carries IOCB_DSYNC and every segment inherits it, so generic_write_sync() runs a range fsync after each segment: up to three cache flushes and log forces per WRITE. Strip IOCB_DSYNC and IOCB_SYNC from the per-segment flags of a split WRITE, and of an unsplit buffered WRITE, and persist the WRITE once with vfs_fsync_range() over the bytes actually written, after the last segment. Durability is unchanged: the reply is not sent until the fsync completes, and datasync mirrors the previous per-segment choice (IOCB_SYNC present means metadata too). An fsync failure is returned like a write failure. A WRITE issued whole as direct I/O keeps its flags: iomap already completes it in one step, and can complete a DATA_SYNC overwrite of allocated blocks with FUA writes and no cache flush. Besides the fewer flushes, the sync now runs after the last segment is written. A later commit relies on that order: it marks the page shared with a neighbouring WRITE for dropping only after writing it, and the WRITE's own fsync is then the writeback that drops the page. Assisted-by: LLM Signed-off-by: Mike Snitzer --- .../filesystems/nfs/nfsd-io-modes.rst | 4 +++- fs/nfsd/vfs.c | 20 ++++++++++++++++++- 2 files changed, 22 insertions(+), 2 deletions(-) diff --git a/Documentation/filesystems/nfs/nfsd-io-modes.rst b/Documentation/filesystems/nfs/nfsd-io-modes.rst index 90bf1038453cc..c1cc974640cfe 100644 --- a/Documentation/filesystems/nfs/nfsd-io-modes.rst +++ b/Documentation/filesystems/nfs/nfsd-io-modes.rst @@ -141,7 +141,9 @@ Misaligned WRITE: has no effect on the O_DIRECT segment unless the filesystem services it with buffered IO instead, as XFS does when it cannot invalidate page cache that overlaps the segment. The iomap_dio_invalidate_fail - trace event reports such a fallback. + trace event reports such a fallback. A split FILE_SYNC or DATA_SYNC + WRITE is persisted once, after all of its segments are written, not + once per segment. If NFSD does not split a misaligned WRITE, it issues the whole WRITE as a single DONTCACHE buffered IO (normal buffered IO if the diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index 7e65328de7c86..249358256d2f5 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -1426,16 +1426,27 @@ nfsd_direct_write(struct svc_rqst *rqstp, struct svc_fh *fhp, { struct nfsd_write_dio_seg segments[3]; struct file *file = nf->nf_file; + loff_t start = kiocb->ki_pos; unsigned int nsegs, i; + int sync_flags; ssize_t host_err; size_t expected; nsegs = nfsd_write_dio_iters_init(nf, rqstp->rq_bvec, nvecs, kiocb, *cnt, segments); + /* + * Persist a synchronous WRITE once, after all of its segments. A + * WRITE issued whole as direct I/O keeps IOCB_DSYNC, so iomap can + * still complete a DATA_SYNC overwrite with FUA writes. + */ + sync_flags = kiocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC); + if (nsegs == 1 && (segments[0].flags & IOCB_DIRECT)) + sync_flags = 0; + *cnt = 0; for (i = 0; i < nsegs; i++) { - kiocb->ki_flags = segments[i].flags; + kiocb->ki_flags = segments[i].flags & ~sync_flags; if (kiocb->ki_flags & IOCB_DIRECT) trace_nfsd_write_direct(rqstp, fhp, kiocb->ki_pos, segments[i].iter.count); @@ -1453,6 +1464,13 @@ nfsd_direct_write(struct svc_rqst *rqstp, struct svc_fh *fhp, break; /* partial write */ } + if (sync_flags && *cnt) { + host_err = vfs_fsync_range(file, start, start + *cnt - 1, + !(sync_flags & IOCB_SYNC)); + if (host_err < 0) + return host_err; + } + return 0; } -- 2.52.0