Re: [PATCH 1/7] memcg : comment, style fixes for recent patch ofmove_parent

[Johannes Weiner]

On Fri, Jan 21, 2011 at 03:37:26PM +0900, KAMEZAWA Hiroyuki wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> 
> A fix for 987eba66e0e6aa654d60881a14731a353ee0acb4
> 
> A clean up for mem_cgroup_move_parent(). 
>  - remove unnecessary initialization of local variable.
>  - rename charge_size -> page_size
>  - remove unnecessary (wrong) comment.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
>  mm/memcontrol.c |   17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> Index: mmotm-0107/mm/memcontrol.c
> ===================================================================
> --- mmotm-0107.orig/mm/memcontrol.c
> +++ mmotm-0107/mm/memcontrol.c
> @@ -2265,7 +2265,7 @@ static int mem_cgroup_move_parent(struct
>  	struct cgroup *cg = child->css.cgroup;
>  	struct cgroup *pcg = cg->parent;
>  	struct mem_cgroup *parent;
> -	int charge = PAGE_SIZE;
> +	int page_size;
>  	unsigned long flags;
>  	int ret;
>  
> @@ -2278,22 +2278,23 @@ static int mem_cgroup_move_parent(struct
>  		goto out;
>  	if (isolate_lru_page(page))
>  		goto put;
> -	/* The page is isolated from LRU and we have no race with splitting */
> -	charge = PAGE_SIZE << compound_order(page);
> +
> +	page_size = PAGE_SIZE << compound_order(page);

Okay, so you remove the wrong comment, but that does not make the code
right.  What protects compound_order from reading garbage because the
page is currently splitting?
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