[Devel] Re: [RFC] memory controller : backgorund reclaim and avoid excessive locking [4/5] borrow resource

[KAMEZAWA Hiroyuki]

On Mon, 18 Feb 2008 09:53:35 +0900 (JST)
yamamoto at valinux.co.jp (YAMAMOTO Takashi) wrote:

> > +		/* try to charge */
> > +		ret = res_counter_charge(&mem->res, mem->borrow_unit);
> > +		if (!ret) { /* success */
> > +			*bwp += (mem->borrow_unit - size);
> > +			goto out;
> > +		}
> > +	}
> > +	spin_lock(&mem->res.lock);
> > +	ret = res_counter_charge_locked(&mem->res, size);
> > +	spin_unlock(&mem->res.lock);
> 
> although i don't know if it matters, this retrying of charge affects failcnt.
> 
Hmm, yes. But what failcnt means is not so clear anyway.


> > +static void mem_cgroup_return_and_uncharge(struct mem_cgroup *mem, int size)
> > +{
> > +	unsigned long flags;
> > +	int uncharge_size = 0;
> > +
> > +	local_irq_save(flags);
> > +	if (mem->borrow_unit) {
> > +		int limit = mem->borrow_unit * 2;
> > +		int cpu;
> > +		s64 *bwp;
> > +		cpu = smp_processor_id();
> > +		bwp = &mem->stat.cpustat[cpu].count[MEM_CGROUP_STAT_BORROW];
> > +		*bwp += size;
> > +		if (*bwp > limit) {
> > +			uncharge_size = *bwp - mem->borrow_unit;
> > +			*bwp = mem->borrow_unit;
> > +		}
> > +	} else
> > +		uncharge_size = size;
> > +
> > +	if (uncharge_size) {
> > +		spin_lock(&mem->res.lock);
> > +		res_counter_uncharge_locked(&mem->res, size);
> 
> s/size/uncharge_size/
> 
Oops...will fix.


> > @@ -1109,12 +1202,29 @@ static u64 mem_throttle_read(struct cgro
> >  	return (u64)mem->throttle.limit;
> >  }
> >  
> > +static int mem_bulkratio_write(struct cgroup *cont, struct cftype *cft, u64 val)
> > +{
> > +	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
> > +	int unit = val * PAGE_SIZE;
> > +	if (unit > (PAGE_SIZE << (MAX_ORDER/2)))
> > +		return -EINVAL;
> > +	mem->borrow_unit = unit;
> > +	return 0;
> > +}
> 
> it seems unsafe with concurrent mem_cgroup_borrow_and_charge or
> mem_cgroup_return_and_uncharge.
> 
Hmm, making this to be not configurable will be good.

Thanks,
-Kame

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