Re: [RFC][PATCH] memcg remove css_get/put per pages v2

[KAMEZAWA Hiroyuki]

On Fri, 11 Jun 2010 11:41:02 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-06-09 15:59:40]:
> 
> > +		if (consume_stock(mem)) {
> > +			/*
> > +			 * It seems dagerous to access memcg without css_get().
> > +			 * But considering how consume_stok works, it's not
> > +			 * necessary. If consume_stock success, some charges
> > +			 * from this memcg are cached on this cpu. So, we
> > +			 * don't need to call css_get()/css_tryget() before
> > +			 * calling consume_stock().
> > +			 */
> > +			rcu_read_unlock();
> > +			goto done;
> > +		}
> > +		if (!css_tryget(&mem->css)) {
> 
> If tryget fails, can one assume that this due to a race and the mem is
> about to be freed?
> 
Yes. it's due to a race and "mem" will be no longer used.
This does the same thing which try_get_mem_cgrou_from_mm() does now.

Thanks,
-Kame

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