linux-kernel - Re: [PATCH] memcg: change behavior of moving charges at task move

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Message-Id: <20120322143610.e4df49c9.akpm@linux-foundation.org>
Date:	Thu, 22 Mar 2012 14:36:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Hugh Dickins <hughd@...gle.com>,
	"n-horiguchi@...jp.nec.com" <n-horiguchi@...jp.nec.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Glauber Costa <glommer@...allels.com>
Subject: Re: [PATCH] memcg: change behavior of moving charges at task move

On Wed, 21 Mar 2012 18:52:04 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

>  static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
>  			unsigned long addr, pte_t ptent, swp_entry_t *entry)
>  {
> -	int usage_count;
>  	struct page *page = NULL;
>  	swp_entry_t ent = pte_to_swp_entry(ptent);
>  
>  	if (!move_anon() || non_swap_entry(ent))
>  		return NULL;
> -	usage_count = mem_cgroup_count_swap_user(ent, &page);
> -	if (usage_count > 1) { /* we don't move shared anon */
> -		if (page)
> -			put_page(page);
> -		return NULL;
> -	}
> +#ifdef CONFIG_SWAP
> +	/*
> +	 * Avoid lookup_swap_cache() not to update statistics.
> +	 */

I don't understand this comment - what is it trying to tell us?

> +	page = find_get_page(&swapper_space, ent.val);

The code won't even compile if CONFIG_SWAP=n?

> +#endif
>  	if (do_swap_account)
>  		entry->val = ent.val;
>  
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