Re: Strange performance change 59 -> 61/62

[Andrew Morton <akpm@digeo.com>]

"Martin J. Bligh" <mbligh@aracnet.com> wrote:
>
> > mark_inode_dirty() tends to be called _very_ frequently.  Too frequently.
> > 
> > Could you try remounting all filesystems noatime with
> > 
> > 	mount /mnt/point -o remount,noatime
> > 
> > and the below patch will prevent us calling the barrier-happy
> > current_kernel_time() for noatime mounts.
> 
> Cool, that works nicely - thanks.
> 
> 2.5.59-mjb6:             84 __mark_inode_dirty
> 2.5.61-mjb1:            594 __mark_inode_dirty
> 2.5.61-mjb1-no_mb:       74 __mark_inode_dirty
> 2.5.61-mjb1-noatime:     65 __mark_inode_dirty
> 

OK.  We used to only run mark_inode_dirty() for atime updates just when it
had actually changed.  ie: once per second.  But for reasons which remain
obscure that was taken out.

This probably explains your ext3 woes.  Poor old ext3 has to do a ton of work
in ext3_mark_inode_dirty(), yet on 99% of the calls, nothing has even
changed.  Which is why I suggested that you retest ext3 with noatime.

I shall fix it up.