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 D412D2F260C; Mon, 9 Mar 2026 17:40:09 +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=1773078009; cv=none; b=K/MqP8STEAIrdv5b8kh6SVikpIj4eoaUQj7ooJoxR4FYZkzoBY9I7Hx917x4+2pu6Muo4AfR+vLqiKC+9y/BOCcejh4K4UT0l+Q58qXLZ5JYnnnjFBBQL3+oMS9ZMG7hj4EFj1KApW9haSafDcjKKZhGbTqfLTy8xFBCUp0Obn8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773078009; c=relaxed/simple; bh=xCB1rLERH4O4/XL0uHe/faGStCm8QjO0kIi2lwkxDkY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=RBjukYBWh9XrX90RBxPQPjhosi9d5gWaqi5dpJ1IWRNuw1Z8UTH3jiwMC8F8nN3h7zf9KTrdfDzPpS4h5MciQOW4jqezwU43rlT15I4CiJPnhSFl+//aVYJlRINxUUvtHe28h/F4UjlMYHuX12fKaPJowrmh1Y4Ux3E1UqGmPDs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pE0YFeqk; 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="pE0YFeqk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 718D6C4CEF7; Mon, 9 Mar 2026 17:40:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773078009; bh=xCB1rLERH4O4/XL0uHe/faGStCm8QjO0kIi2lwkxDkY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pE0YFeqkP1myKJB9xLPp8PNR5Dhyvp6zEOUY0Jy2sbjCKpD+paZE8VG4dnfABQkoZ 4vPj5k2KnRlLeTiNW40oSE7pAN2o8N19l8wgSLUG301GctaZz85WgdiCGHENDKUA5U tb5EDki4z08OoL38F4ScMOkPMfCR7esLahuJGwUgW74OENsOdEgiwj0zTHg5YaHzpL /k95Q+lYNBmFLsh0jLgJK9kSfrqABb5/eP4pIzX9Jl8hfFqbr4gepuMtJSTgJJS6qA 9e4ysswZ0MpSyV9Pw1MIl2MTO9Vl+ge04th61ic9TY4yq5Sy7dhKPw7VdZnChShjlc +eGsVKXVZRvLQ== Date: Mon, 9 Mar 2026 10:40:08 -0700 From: "Darrick J. Wong" To: Brian Foster Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH v3 3/8] iomap, xfs: lift zero range hole mapping flush into xfs Message-ID: <20260309174008.GO6033@frogsfrogsfrogs> References: <20260309134506.167663-1-bfoster@redhat.com> <20260309134506.167663-4-bfoster@redhat.com> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260309134506.167663-4-bfoster@redhat.com> On Mon, Mar 09, 2026 at 09:45:01AM -0400, Brian Foster wrote: > iomap zero range has a wart in that it also flushes dirty pagecache > over hole mappings (rather than only unwritten mappings). This was > included to accommodate a quirk in XFS where COW fork preallocation > can exist over a hole in the data fork, and the associated range is > reported as a hole. This is because the range actually is a hole, > but XFS also has an optimization where if COW fork blocks exist for > a range being written to, those blocks are used regardless of > whether the data fork blocks are shared or not. For zeroing, COW > fork blocks over a data fork hole are only relevant if the range is > dirty in pagecache, otherwise the range is already considered > zeroed. > > The easiest way to deal with this corner case is to flush the > pagecache to trigger COW remapping into the data fork, and then > operate on the updated on-disk state. The problem is that ext4 > cannot accommodate a flush from this context due to being a > transaction deadlock vector. > > Outside of the hole quirk, ext4 can avoid the flush for zero range > by using the recently introduced folio batch lookup mechanism for > unwritten mappings. Therefore, take the next logical step and lift > the hole handling logic into the XFS iomap_begin handler. iomap will > still flush on unwritten mappings without a folio batch, and XFS > will flush and retry mapping lookups in the case where it would > otherwise report a hole with dirty pagecache during a zero range. > > Note that this is intended to be a fairly straightforward lift and > otherwise not change behavior. Now that the flush exists within XFS, > follow on patches can further optimize it. > > Signed-off-by: Brian Foster > --- > fs/iomap/buffered-io.c | 2 +- > fs/xfs/xfs_iomap.c | 25 ++++++++++++++++++++++--- > 2 files changed, 23 insertions(+), 4 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index bc82083e420a..0999aca6e5cc 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -1642,7 +1642,7 @@ iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero, > srcmap->type == IOMAP_UNWRITTEN)) { > s64 status; > > - if (range_dirty) { > + if (range_dirty && srcmap->type == IOMAP_UNWRITTEN) { > range_dirty = false; > status = iomap_zero_iter_flush_and_stale(&iter); > } else { > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c > index 0e323e4e304b..966fb9d8b9df 100644 > --- a/fs/xfs/xfs_iomap.c > +++ b/fs/xfs/xfs_iomap.c > @@ -1811,6 +1811,7 @@ xfs_buffered_write_iomap_begin( > if (error) > return error; > > +restart: > error = xfs_ilock_for_iomap(ip, flags, &lockmode); > if (error) > return error; > @@ -1838,9 +1839,27 @@ xfs_buffered_write_iomap_begin( > if (eof) > imap.br_startoff = end_fsb; /* fake hole until the end */ > > - /* We never need to allocate blocks for zeroing or unsharing a hole. */ > - if ((flags & (IOMAP_UNSHARE | IOMAP_ZERO)) && > - imap.br_startoff > offset_fsb) { > + /* We never need to allocate blocks for unsharing a hole. */ > + if ((flags & IOMAP_UNSHARE) && imap.br_startoff > offset_fsb) { > + xfs_hole_to_iomap(ip, iomap, offset_fsb, imap.br_startoff); > + goto out_unlock; > + } > + > + /* > + * We may need to zero over a hole in the data fork if it's fronted by > + * COW blocks and dirty pagecache. To make sure zeroing occurs, force > + * writeback to remap pending blocks and restart the lookup. > + */ > + if ((flags & IOMAP_ZERO) && imap.br_startoff > offset_fsb) { > + if (filemap_range_needs_writeback(inode->i_mapping, offset, > + offset + count - 1)) { > + xfs_iunlock(ip, lockmode); > + error = filemap_write_and_wait_range(inode->i_mapping, > + offset, offset + count - 1); Two tab indent here, but other than that nit this makes sense to me. Reviewed-by: "Darrick J. Wong" --D > + if (error) > + return error; > + goto restart; > + } > xfs_hole_to_iomap(ip, iomap, offset_fsb, imap.br_startoff); > goto out_unlock; > } > -- > 2.52.0 > >