preallocate CPU usage - pre4
matt at mattmccutchen.net
Sun Nov 18 18:45:01 GMT 2007
On Mon, 2007-11-05 at 06:25 -0700, Rob Bosch wrote:
> When I use the preallocate patch and create a 77GB file using the function I
> get a CPU spike on the server-side.
I don't think reproducing the CPU spike on Linux will be meaningful
because Linux treats posix_fallocate differently from Cygwin: Cygwin
just reserves space for the file while Linux actually writes a byte into
every disk block of the file. We need to figure out why rsync on your
Cygwin is giving a different result from Corinna's Cygwin.
I did notice that the preallocation code incorrectly uses 32-bit ints
for some file offsets; it should use OFF_Ts. The attached patch fixes
this. However, the mistake didn't affect the main call to
posix_fallocate, so it doesn't explain the problem you are having.
Here are two things I suggest that you try:
1. Strace rsync and make sure posix_fallocate is getting called with the
2. Write your own program that allocates a 77GB file with
posix_fallocate and see if the same thing happens.
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