Re: [RFC] [PATCH 3/4] Reclaim from groups over their soft limit under memory pressure

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

On Wed, 13 Feb 2008 20:42:42 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> 
> +	read_lock_irqsave(&mem_cgroup_sl_list_lock, flags);
> +	while (!list_empty(&mem_cgroup_sl_exceeded_list)) {
> +		mem = list_first_entry(&mem_cgroup_sl_exceeded_list,
> +				struct mem_cgroup, sl_exceeded_list);
> +		list_move(&mem->sl_exceeded_list, &reclaimed_groups);
> +		read_unlock_irqrestore(&mem_cgroup_sl_list_lock, flags);
> +
> +		nr_bytes_over_sl = res_counter_sl_excess(&mem->res);
> +		if (nr_bytes_over_sl <= 0)
> +			goto next;
> +		nr_pages = (nr_bytes_over_sl >> PAGE_SHIFT);
> +		ret += try_to_free_mem_cgroup_pages(mem, gfp_mask, nr_pages,
> +							zones);
> +next:
> +		read_lock_irqsave(&mem_cgroup_sl_list_lock, flags);

Hmm... 
This is triggered by page allocation failure (fast path) in alloc_pages()
after try_to_free_pages(). Then, what pages should be reclaimed is 
depends on zones[]. Because nr-bytes_over_sl is counted globally, cgroup's
pages may not be included in zones[].

And I think it's big workload to relclaim all excessed pages at once.

How about just reclaiming small # of pages ? like
==
if (nr_bytes_over_sl <= 0)
	goto next;
nr_pages = SWAP_CLUSTER_MAX;
==

Regards,
-Kame




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