[Devel] Re: [RFC 4/4] memcg: NUMA background reclaim

[KAMEZAWA Hiroyuki]

On Tue, 27 May 2008 22:56:43 +0530
Balbir Singh <balbir at linux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > One aspect of difference in reclaim logic between global lru and memcg is 
> >  * global LRU triggers memory reclaim at memory shortage.
> >  * memcg LRU triggers memory reclaim at excess of usage.
> > 
> > Then, global LRU _know_ which node we should start reclaim from.
> >  * start from a node at memory shortage or
> >  * start from a node where memory allocation is waiting
> > 
> > WRT memcg, it's difficult to find where we should start because
> > there is no memory shortage and LRU is splitted.
> > (But per-zone-LRU is definitely necessary for scalability.)
> > 
> > This patch tries to deteremine a node for starting recalim by checking
> > ratio of inactive pages/active pages in a node. And trying to avoid starting
> > from a node with relatively small usage.
> > Better algorithm is welcome.
> > 
> > Singed-off-by: KAMEZAWA Hiruyuki <kamezawa.hiroyu at jp.fujitsu.com>
> > 
> > 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
> > @@ -578,7 +578,7 @@ retry:
> >  	if (state == RES_OVER_LIMIT) {
> >  		if (!(gfp_mask & __GFP_WAIT))
> >  			goto out;
> > -		if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> > +		if (try_to_free_mem_cgroup_pages(mem, -1, gfp_mask))
> >  			goto retry;
> >  		/*
> >  		 * try_to_free_mem_cgroup_pages() might not give us a
> > @@ -801,7 +801,7 @@ int mem_cgroup_shrink_usage(struct mm_st
> >  	rcu_read_unlock();
> > 
> >  	do {
> > -		progress = try_to_free_mem_cgroup_pages(mem, gfp_mask);
> > +		progress = try_to_free_mem_cgroup_pages(mem, -1, gfp_mask);
> >  	} while (!progress && --retry);
> > 
> >  	if (!retry)
> > @@ -814,7 +814,7 @@ static void mem_cgroup_drop_all_pages(st
> >  {
> >  	int progress;
> >  	while (!res_counter_empty(&mem->res)) {
> > -		progress = try_to_free_mem_cgroup_pages(mem,
> > +		progress = try_to_free_mem_cgroup_pages(mem, -1,
> >  					GFP_HIGHUSER_MOVABLE);
> >  		if (!progress) /* we did as much as possible */
> >  			break;
> > @@ -912,6 +912,62 @@ out:
> >  /*
> >   * background reclaim daemon.
> >   */
> > +
> > +#ifdef CONFIG_NUMA
> > +/*
> > + * Because memory controller's memory reclaim doesn't come from memory shortage,
> > + * we cannot know which node should be reclaimed in an easy way.
> > + * This routine select a node with inactive pages to be a node for starting
> > + * scanning.
> > + */
> > +int __select_best_node(struct mem_cgroup *mem)
> > +{
> > +	int nid;
> > +	int best_node = -1;
> > +	unsigned long highest_inactive_ratio = 0;
> > +	unsigned long active, inactive, inactive_ratio, total, threshold, flags;
> > +	struct mem_cgroup_per_zone *mz;
> > +	int zid;
> > +
> > +	/*
> > +	 * When a node's memory usage is smaller than 
> > +  	 * total_usage/num_of_node * 75%, we don't select the node
> > +	 */
> > +	total = mem->res.usage >> PAGE_SHIFT;
> > +	threshold = (total / num_node_state(N_HIGH_MEMORY)) * 3 / 4;
> > +
> > +	/*
> > +	 * See nodemask.h, N_HIGH_MEMORY means that a node has memory
> > +	 * can be used for user's memory.(i.e. not means HIGHMEM).
> > +	 */
> > +	for_each_node_state(nid, N_HIGH_MEMORY) {
> > +		active = 0;
> > +		inactive = 0;
> > +
> > +		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> > +			mz = mem_cgroup_zoneinfo(mem, nid, zid);
> > +			spin_lock_irqsave(&mz->lru_lock, flags);
> > +			active += MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_ACTIVE);
> > +			inactive +=
> > +				MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE);
> > +			spin_unlock_irqrestore(&mz->lru_lock, flags);
> > +		}
> > +
> > +		if (active + inactive < threshold)
> > +			continue;
> > +		inactive_ratio = (inactive * 100) / (active + 1);
> > +		if (inactive_ratio > highest_inactive_ratio)
> > +			best_node = nid;
> 
> Shouldn't we update highest_inactive_ration here?
> 
AH, yes. blame me :( Thanks!

Thanks,
-Kame

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