lkml.org 
[lkml]   [2010]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] writeback: remove the internal 5% low bound on dirty_ratio
On Fri, 20 Aug 2010 15:50:54 +1000
Con Kolivas <kernel@kolivas.org> wrote:

> On Fri, 20 Aug 2010 02:13:25 pm KOSAKI Motohiro wrote:
> > > The dirty_ratio was silently limited to >= 5%. This is not a user
> > > expected behavior. Let's rip it.
> > >
> > > It's not likely the user space will depend on the old behavior.
> > > So the risk of breaking user space is very low.
> > >
> > > CC: Jan Kara <jack@suse.cz>
> > > CC: Neil Brown <neilb@suse.de>
> > > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> >
> > Thank you.
> > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>
> I have tried to do this in the past, and setting this value to 0 on some
> machines caused the machine to come to a complete standstill with small
> writes to disk. It seemed there was some kind of "minimum" amount of data
> required by the VM before anything would make it to the disk and I never
> quite found out where that blockade occurred. This was some time ago (3 years
> ago) so I'm not sure if the problem has since been fixed in the VM since
> then. I suggest you do some testing with this value set to zero before
> approving this change.
>

If it is appropriate to have a lower limit, that should be imposed where
the sysctl is defined in kernel/sysctl.c, not imposed after the fact where
the value is used.

As we now have dirty_bytes which over-rides dirty_ratio, there is little
cost in having a lower_limit for dirty_ratio - it could even stay at 5% -
but it really shouldn't be silent. Writing a number below the limit to the
sysctl file should fail.

NeilBrown


\
 
 \ /
  Last update: 2010-08-23 06:45    [W:0.193 / U:0.728 seconds]
©2003-2014 Jasper Spaans. Advertise on this site