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On 6/28/12 11:12 AM, Phillip Susi wrote:

On 6/25/2012 3:33 AM, Andreas Dilger wrote:

quoted

There was a recent patch series "ext4: add an io-tree to track
block allocation" that may improve the performance for your case of
overwrite of uninitialized files, but it hasn't landed yet.

I'm confused.  Why is writing to uninitialized extents slow, and why
would this help?  If you have an uninitialized extent, then the blocks
are already allocated, just flagged as containing uninitialized data.
 Writing to them should be no different than writing to initialized
extents, save for the step of clearing the uninitialized flag.

The other piece is that large uninitialized extents get split into
up to 3 extents if you write into the middle of them so there are
potentially a lot more metadata updates flying around.

- -Eric
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