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

Andrew Morton
2012-03-23T00:26:46Z

On Fri, 23 Mar 2012 09:18:46 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> >> +#ifdef CONFIG_SWAP
> >> + /*
> >> + * Avoid lookup_swap_cache() not to update statistics.
> >> + */
> >
> > I don't understand this comment - what is it trying to tell us?
> >
>
>
> High Dickins advised me to use find_get_page() rather than lookup_swap_cache()
> because lookup_swap_cache() has some statistics with swap.

ah.

--- a/mm/memcontrol.c~memcg-change-behavior-of-moving-charges-at-task-move-fix
+++ a/mm/memcontrol.c
@@ -5137,7 +5137,8 @@ static struct page *mc_handle_swap_pte(s
return NULL;
#ifdef CONFIG_SWAP
/*
- * Avoid lookup_swap_cache() not to update statistics.
+ * Use find_get_page() rather than lookup_swap_cache() because the
+ * latter alters statistics.
*/
page = find_get_page(&swapper_space, ent.val);
#endif

> >> + page = find_get_page(&swapper_space, ent.val);
> >
> > The code won't even compile if CONFIG_SWAP=n?
> >
>
> mm/built-in.o: In function `mc_handle_swap_pte':
> /home/kamezawa/Kernel/next/linux/mm/memcontrol.c:5172: undefined reference to `swapper_space'
> make: *** [.tmp_vmlinux1] Error 1
>
> Ah...but I think this function (mc_handle_swap_pte) itself should be under CONFIG_SWAP.
> I'll post v2.

Confused. The new reference to swapper_space is already inside #ifdef
CONFIG_SWAP.