Re: [PATCH 05/18] writeback: per task dirty rate limit

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Tue 06-09-11 17:47:10, Peter Zijlstra wrote:
> On Sun, 2011-09-04 at 09:53 +0800, Wu Fengguang wrote:
> >  /*
> > + * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
> > + * will look to see if it needs to start dirty throttling.
> > + *
> > + * If dirty_poll_interval is too low, big NUMA machines will call the expensive
> > + * global_page_state() too often. So scale it near-sqrt to the safety margin
> > + * (the number of pages we may dirty without exceeding the dirty limits).
> > + */
> > +static unsigned long dirty_poll_interval(unsigned long dirty,
> > +                                        unsigned long thresh)
> > +{
> > +       if (thresh > dirty)
> > +               return 1UL << (ilog2(thresh - dirty) >> 1);
> > +
> > +       return 1;
> > +}
> 
> Where does that sqrt come from? 
  He does 2^{log_2(x)/2} which, if done in real numbers arithmetics, would
result in x^{1/2}. Given the integer arithmetics, it might be twice as
small but still it's some approximation...

									Honza
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux