Re: [PATCH] ext4: do not normalize block requests from fallocate.

From: Ted Ts'o
Date: Sun May 22 2011 - 21:11:35 EST

On Fri, May 13, 2011 at 02:19:05PM -0700, Vivek Haldar wrote:
> Currently, an fallocate request of size slightly larger than a power of
> 2 is turned into two block requests, each a power of 2, with the extra
> blocks pre-allocated for future use. When an application calls
> fallocate, it already has an idea about how large the file may grow so
> there is usually little benefit to reserve extra blocks on the
> preallocation list. This reduces disk fragmentation.
> Tested: fsstress. Also verified manually that fallocat'ed files are
> contiguously laid out with this change (whereas without it they begin at
> power-of-2 boundaries, leaving blocks in between). CPU usage of
> fallocate is not appreciably higher. In a tight fallocate loop, CPU
> usage hovers between 5%-8% with this change, and 5%-7% without it.
> Signed-off-by: Vivek Haldar <haldar@xxxxxxxxxx>

Applied, with a minor change to avoid a bit assignment conflict with
the punch patches.

Also, I changed the commit message to note that using a file aging
simulator which filled the file system to 70%, the percentage of free
extents greater than 8MB (as measured using e2freefrag) increased from
38.8% without this commit, to 69.4% with this commit.

- Ted
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