Re: [RFC 2/4] memcg: high-low watermark

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 27 May 2008 21:56:17 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > Add high/low watermarks to res_counter.
> > *This patch itself has no behavior changes to memory resource controller.
> > 
> > Changelog: very old one -> this one (v1)
> >  - watarmark_state is removed and all state check is done under lock.
> >  - changed res_counter_charge() interface. The only user is memory
> >    resource controller. Anyway, returning -ENOMEM here is a bit starnge.
> >  - Added watermark enable/disable flag for someone don't want watermarks.
> >  - Restarted against 2.6.25-mm1.
> >  - some subsystem which doesn't want high-low watermark can work withou it.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > From: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
> > 
> 
> The From: line should be the first line IIRC.
> 
ok.

>
> >  	/*
> > +	 * watermarks. needs to keep lwmark <= hwmark <= limit.
> > +	 */
> > +	unsigned long long hwmark;
> > +	unsigned long long lwmark;
> > +	int		   use_watermark;
> 
> Is it routine to comment this way? I prefer not to have spaces in the type and
> the member, makes it easier for my eyes.
> 
Hmm. will fix.




> > + * RES_BELOW_LIMIT  --  usage is smaller than limt, success.
> 
> 						^^^^ typo
> 
sure, will fix.



> > +	spin_unlock_irqrestore(&counter->lock, flags);
> > +	return ret;
> > +}
> > +
> 
> When do we return RES_OVER_LIMIT? Are we missing that here?
> 
It's Bug. Yamamoto-san pointed out and I'm now fixing.


> >  	spin_lock_irqsave(&counter->lock, flags);
> > +	switch (member) {
> > +		case RES_LIMIT:
> > +			if (counter->use_watermark && counter->hwmark > tmp)
> > +				goto unlock_free;
> 
> We need to document such API changes in the Documentation/controllers/memory.txt
> file.
> 
ok, I'll add patch for documentation. to memory.txt and res_counter.txt.


> > +			break;
> > +		case RES_HWMARK:
> > +			if (tmp < counter->lwmark  || tmp > counter->limit)
> > +				goto unlock_free;
> > +			break;
> > +		case RES_LWMARK:
> > +			if (tmp > counter->hwmark)
> > +				goto unlock_free;
> > +			break;
> > +		default:
> > +			break;
> > +	}
> >  	val = res_counter_member(counter, member);
> >  	*val = tmp;
> > -	spin_unlock_irqrestore(&counter->lock, flags);
> >  	ret = nbytes;
> > +unlock_free:
> > +	spin_unlock_irqrestore(&counter->lock, flags);
> >  out_free:
> >  	kfree(buf);
> >  out:
> > Index: mm-2.6.26-rc2-mm1/mm/memcontrol.c
> > ===================================================================
> > --- mm-2.6.26-rc2-mm1.orig/mm/memcontrol.c
> > +++ mm-2.6.26-rc2-mm1/mm/memcontrol.c
> > @@ -559,7 +559,7 @@ static int mem_cgroup_charge_common(stru
> >  		css_get(&memcg->css);
> >  	}
> > 
> > -	while (res_counter_charge(&mem->res, PAGE_SIZE)) {
> > +	while (res_counter_charge(&mem->res, PAGE_SIZE) == RES_OVER_LIMIT) {
> >  		if (!(gfp_mask & __GFP_WAIT))
> >  			goto out;
> > 
> 
> Otherwise looks good so far. Need to look at the background reclaim code.
> 

Thanks,
-Kame

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