Re: [RFC] Reduce the resource counter lock overhead

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-06-25 13:39:08]:

> On Wed, 24 Jun 2009 20:44:26 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Thu, 25 Jun 2009 08:57:17 +0530 Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > 
> > > We do a read everytime before we charge.
> > 
> > See, a good way to fix that is to not do it.  Instead of
> > 
> > 	if (under_limit())
> > 		charge_some_more(amount);
> > 	else
> > 		goto fail;
> > 
> > one can do 
> > 
> > 	if (try_to_charge_some_more(amount) < 0)
> > 		goto fail;
> > 
> > which will halve the locking frequency.  Which may not be as beneficial
> > as avoiding the locking altogether on the read side, dunno.
> > 
> I don't think we do read-before-write ;)
>

I need to figure out the reason for read contention and why seqlock's
help. Like I said before I am seeing some strange values for
reclaim_stats on the root cgroup, even though it is not reclaimable or
not used for reclaim. There can be two reasons

1. Reclaim
2. User space constantly reading the counters

I have no user space utilities I am aware of running on the system,
constantly reading the contents of the files. 

-- 
	Balbir

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