Re: [PATCH][for -mm] Fix and Enhancements for memory cgroup [6/6] add force reclaim interface

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

On Wed, 10 Oct 2007 00:14:53 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > This patch adds an interface "memory.force_reclaim".
> > Any write to this file will drop all charges in this cgroup if
> > there is no task under.
> > 
> > %echo 1 > /....../memory.force_reclaim
> > 
> 
> Looks like a good name, do you think system administrators would
> find force_empty more useful?
> 
good name :) I'll use it.


> > +static void
> > +mem_cgroup_force_reclaim_list(struct mem_cgroup *mem, struct list_head *list)
> > +{
> > +	struct page_cgroup *pc;
> > +	struct page *page;
> > +	int count = SWAP_CLUSTER_MAX;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&mem->lru_lock, flags);
> > +
> 
> Can we add a comment here stating that this routine reclaims just
> from the per cgroup LRU and not from the zone LRU to which the
> page belongs.
> 
Ok.

> > +	while (!list_empty(list)) {
> > +		pc = list_entry(list->prev, struct page_cgroup, lru);
> > +		page = pc->page;
> > +		if (clear_page_cgroup(page, pc) == pc) {
> > +			css_put(&mem->css);
> > +			res_counter_uncharge(&mem->res, PAGE_SIZE);
> > +			list_del_init(&pc->lru);
> > +			kfree(pc);
> > +		} else
> > +			count = 1; /* race? ...do relax */
> > +
> > +		if (--count == 0) {
> > +			spin_unlock_irqrestore(&mem->lru_lock, flags);
> > +			cond_resched();
> > +			spin_lock_irqsave(&mem->lru_lock, flags);
> > +			count = SWAP_CLUSTER_MAX;
> > +		}
> > +	}
> > +	spin_unlock_irqrestore(&mem->lru_lock, flags);
> > +}
> > +
> > +int mem_cgroup_force_reclaim(struct mem_cgroup *mem)
> > +{
> > +	int ret = -EBUSY;
> > +	while (!list_empty(&mem->active_list) ||
> > +	       !list_empty(&mem->inactive_list)) {
> > +		if (atomic_read(&mem->css.cgroup->count) > 0)
> > +			goto out;
> > +		mem_cgroup_force_reclaim_list(mem, &mem->active_list);
> > +		mem_cgroup_force_reclaim_list(mem, &mem->inactive_list);
> > +	}
> > +	ret = 0;
> > +out:
> > +	css_put(&mem->css);
> 
> We do a css_put() here, did we do a css_get() anywhere?
> 
Good catch. it is a BUG. I'll fix.

Thanks,
-Kame

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