Re: Where all does preallocated/extra space hide?

[Eric Sandeen <sandeen@redhat.com>]

Eric Sandeen wrote:
> I was running some of the xfstests enospc tests on ext4, and they were
> failing; in one case, manymanymany small files are made to fill up a
> 100M filesystem.  ext4 stops quite early with -ENOSPC, but after a bit,
> (or after a "sync") we get 40MB free again.  So 40% of the fs space is
> hidden somewhere in preallocation...
> 
> I tried calling out to discard group prealloc but that's only a few
> blocks.  I'll go trace through the sync paths to see what all gets
> released, but if anyone knows offhand where the rest of that space is
> hiding, please give me a shout.  :)
> 
> Thanks,
> -Eric

Possibly related; on a 1G filesystem, doing this:

#!/bin/bash

xfs_io -F -f -d -c 'pwrite -b 64k 0 512m' /mnt/test/io_test
rm /mnt/test/io_test

in a "while true" loop spews ENOSPC.  (it's a direct IO 512m write in 
64k chunks).  Buffered IO seems fine ...

-Eric