Re: [PATCH 0/2] Re: Discrepancy in 'df' output between kernel 3.0 and 3.2 for ext4?

[Ted Ts'o <tytso@mit.edu>]

On Tue, Jun 19, 2012 at 02:54:44PM -0500, Zachary Mark wrote:
> 
> Ted, thanks for the patches!  I've tested your patches against
> 3.5~rc3.  I had to return the machine on which I first spotted the
> problem, but here are results from a box with identical hardware:
> 
> df from 3.0:
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdh1            2907178636    205816 2906972820   1%
> /dev/sdi1            2907178636   1056768 2906121868   1%
> 
> df from 3.2.20 (identical to 3.5~rc3 without your patches):
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdh1            2928733612  21760792 2906972820   1%
> /dev/sdi1            2928733612  22611744 2906121868   1%
> 
> 
> df from 3.5~rc3 with your patches applied (as they didn't apply to 3.2):
> /dev/sdh1            2907178636    205816 2906972820   1%
> /dev/sdi1            2907178636   1060936 2906117700   1%
> 
> sdh1 is mostly empty.  sdi1 has about 6700 128k files written to it plus
> everything on sdh1.  There seems to be slightly more overhead accounted
> for after your patches.  Not sure if this is to be expected or not.

Hmm... it looks like df output /dev/sdh1 is identical between 3.0 and
3.5~rc3 with my patches.  I'm not sure why there is a difference for
/dev/sdi1.  However, I note that the "Available" figure is the same
between 3.0, 3.2.20 and 3.5~rc3 for /dev/sdh1, but there is a
difference in the Available column between 3.2.20 and 3.5~rc3 for
/dev/sdi3.  Could it be that some files got written to /dev/sdi
between your test run?

It would be good if we could get this sorted out.  I was pretty
careful to account for all of the fs overhead blocks between when I
did my patch with an empty file system.

If this can't be accounted by more files being written to /dev/sdi1,
could you send me the (compressed, since they will be large) output of
dumpe2fs for /dev/sdh1 and /dev/sdi1 with the "df" output from your
three test kernel so I can investigate further?

Thanks,

						- Ted