Re: [PATCH 1/2] writeback: Improve busyloop prevention

[Wu Fengguang <fengguang.wu@intel.com>]

On Thu, Oct 20, 2011 at 08:33:00PM +0800, Wu Fengguang wrote:
> On Thu, Oct 20, 2011 at 08:09:09PM +0800, Wu Fengguang wrote:
> > Jan,
> > 
> > I tried the below combined patch over the ioless one, and find some
> > minor regressions. I studied the thresh=1G/ext3-1dd case in particular
> > and find that nr_writeback and the iostat avgrq-sz drops from time to time.
> > 
> > I'll try to bisect the changeset.

This is interesting, the culprit is found to be patch 1, which is
simply
                if (work->for_kupdate) {
                        oldest_jif = jiffies -
                                msecs_to_jiffies(dirty_expire_interval * 10);
-                       work->older_than_this = &oldest_jif;
-               }
+               } else if (work->for_background)
+                       oldest_jif = jiffies;

Thanks,
Fengguang