From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Eric Sandeen <sandeen@sandeen.net>,
Thomas Lynema <lyz27@yahoo.com>,
xfs@oss.sgi.com
Subject: Re: Poor performance using discard
Date: Thu, 1 Mar 2012 01:31:13 -0500 [thread overview]
Message-ID: <20120301063113.GA15854@infradead.org> (raw)
In-Reply-To: <20120301062709.GB5091@dastard>
On Thu, Mar 01, 2012 at 05:27:09PM +1100, Dave Chinner wrote:
> One other thing the ext4 tracing implementation does is merge
> adjacent ranges, whereas the XFS implementation does not. XFS has
> more tracking complexity than ext4, though, in that it tracks free
> extents in multiple concurrent journal commits whereas ext4 only has
> to track across a single journal commit. Hence ext4 can merge
> without having to care about where the adjacent range is being
> committed in the same journal checkpoint.
>
> Further, ext4 doesn't reallocate from the freed extents until after
> the journal commit completes, whilst XFS can reallocate freed ranges
> before the freeing is journalled and hence can modify ranges in the
> free list prior to journal commit.
>
> We could probably implement extent merging in the free extent
> tracking similar to ext4, but I'm not sure how much it would gain us
> because of the way we do reallocation of freed ranges prior to
> journal commit....
Also there generally aren't that many merging opportunities. Back when
I implemented the code and looked at block traces we'd get them
occasionally:
(a) for inode buffers due to the inode clusters beeing smaller than the
inode chunks. Better fixed by increasing the amount of inode
clustering we do.
(b) during rm -rf sometimes when lots of small files were end-to-end,
but this doesn't happen all that often.
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next prev parent reply other threads:[~2012-03-01 6:31 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-28 22:56 Poor performance using discard Thomas Lynema
2012-02-28 23:58 ` Peter Grandi
2012-02-29 1:22 ` Dave Chinner
2012-02-29 2:00 ` Thomas Lynema
2012-02-29 4:08 ` Dave Chinner
2012-02-29 10:38 ` Peter Grandi
2012-02-29 19:46 ` Eric Sandeen
2012-03-01 5:59 ` Christoph Hellwig
2012-03-01 6:27 ` Dave Chinner
2012-03-01 6:31 ` Christoph Hellwig [this message]
[not found] ` <1330658311.6438.24.camel@core24>
2012-03-02 14:57 ` Thomas Lynema
2012-03-02 15:41 ` Thomas Lynema
2012-03-05 3:02 ` Dave Chinner
2012-03-05 6:41 ` Jeffrey Hundstad
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