From: Christoph Hellwig <hch@lst.de>
To: Brian Foster <bfoster@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
linux-xfs@vger.kernel.org, darrick.wong@oracle.com
Subject: Re: [PATCH 2/3] xfs: go straight to real allocations for direct I/O COW writes
Date: Tue, 24 Jan 2017 17:21:56 +0100 [thread overview]
Message-ID: <20170124162156.GA29361@lst.de> (raw)
In-Reply-To: <20170124161719.GE60234@bfoster.bfoster>
On Tue, Jan 24, 2017 at 11:17:20AM -0500, Brian Foster wrote:
> I thought that while not necessarily guaranteed, generally the entire
> extent gets converted from delalloc to real blocks.
For buffered I/O that's the case. See the discussion on my recent
xfs_bmapi_write patch.
> IIRC, that's what
> I've seen in the past when looking into the cow fork with bmap. After
> all, isn't that the point of the extent size hint? Allocate wider than
> the write to accommodate potential subsequent writes into a more
> contiguous range.
Well, for direct I/O that's not what the current code does. Implementing
it might be useful, but I'm not sure how much the front alignment is
going to help in usual worksloads - you'd need a backwards write or
random writes that happen to look almost backwards for it to make
a difference. I suspect most of them time we'd just allocate blocks to
reclaim them again a little later.
next prev parent reply other threads:[~2017-01-24 16:21 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-05 21:05 reflink COW improvements Christoph Hellwig
2016-12-05 21:05 ` [PATCH 1/3] xfs: reject all unaligned direct writes to reflinked files Christoph Hellwig
2016-12-07 18:59 ` Brian Foster
2016-12-05 21:05 ` [PATCH 2/3] xfs: go straight to real allocations for direct I/O COW writes Christoph Hellwig
2016-12-07 19:00 ` Brian Foster
2016-12-07 19:37 ` Christoph Hellwig
2016-12-07 19:46 ` Brian Foster
2016-12-08 4:23 ` Darrick J. Wong
2017-01-24 8:37 ` Christoph Hellwig
2017-01-24 13:50 ` Brian Foster
2017-01-24 13:59 ` Christoph Hellwig
2017-01-24 15:02 ` Brian Foster
2017-01-24 15:09 ` Christoph Hellwig
2017-01-24 16:17 ` Brian Foster
2017-01-24 16:21 ` Christoph Hellwig [this message]
2017-01-24 17:43 ` Brian Foster
2017-01-24 20:08 ` Christoph Hellwig
2017-01-24 20:10 ` Christoph Hellwig
2017-01-25 0:09 ` Darrick J. Wong
2017-01-27 17:44 ` Darrick J. Wong
2017-01-27 17:48 ` Christoph Hellwig
2016-12-05 21:05 ` [PATCH 3/3] xfs: allocate direct I/O COW blocks in iomap_begin Christoph Hellwig
2016-12-06 2:09 ` reflink COW improvements Darrick J. Wong
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