linux-kernel - Re: [PATCH 7/9] memcg : mem+swap controlelr core

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Date:	Fri, 21 Nov 2008 10:40:07 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	pbadari@...ibm.com, jblunck@...e.de, taka@...inux.co.jp,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/9] memcg : mem+swap controlelr core

> @@ -513,12 +531,25 @@ static int __mem_cgroup_try_charge(struc
>  		css_get(&mem->css);
>  	}
>  
> +	while (1) {

This loop will never break out if memory.limit_in_bytes is too low.

Actually, when I set the limit to 0 and moved a task into the cgroup and let
the task allocate a page, then the whole system froze, and I had to reset
my machine.

And small memory.limit will make the process stuck:
# mkdir /memcg/0
# echo 40K > /memcg/0/memory.limit_in_bytes
# echo $$ > tasks
# ls
(stuck)

(another console)
# echo 100K > /memcg/0/memory.limit_in_bytes
(then the above 'ls' can continue)

> +		int ret;
> +		bool noswap = false;
>  
> -	while (unlikely(res_counter_charge(&mem->res, PAGE_SIZE))) {
> +		ret = res_counter_charge(&mem->res, PAGE_SIZE);
> +		if (likely(!ret)) {
> +			if (!do_swap_account)
> +				break;
> +			ret = res_counter_charge(&mem->memsw, PAGE_SIZE);
> +			if (likely(!ret))
> +				break;
> +			/* mem+swap counter fails */
> +			res_counter_uncharge(&mem->res, PAGE_SIZE);
> +			noswap = true;
> +		}
>  		if (!(gfp_mask & __GFP_WAIT))
>  			goto nomem;
>  
> -		if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> +		if (try_to_free_mem_cgroup_pages(mem, gfp_mask, noswap))
>  			continue;
>  
>  		/*
> @@ -527,8 +558,13 @@ static int __mem_cgroup_try_charge(struc
>  		 * moved to swap cache or just unmapped from the cgroup.
>  		 * Check the limit again to see if the reclaim reduced the
>  		 * current usage of the cgroup before giving up
> +		 *
>  		 */
> -		if (res_counter_check_under_limit(&mem->res))
> +		if (!do_swap_account &&
> +			res_counter_check_under_limit(&mem->res))
> +			continue;
> +		if (do_swap_account &&
> +			res_counter_check_under_limit(&mem->memsw))
>  			continue;
>  
>  		if (!nr_retries--) {


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