Re: [-mm][PATCH 8/10] fix shmem page migration incorrectness on memcgroup

[MinChan Kim]

Hi, KAMEZAWA-san.

I have one question.
It's just curious.

On Wed, Jun 25, 2008 at 7:09 PM, KOSAKI Motohiro
<kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
>
> =
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> mem_cgroup_uncharge() against old page is done after radix-tree-replacement.
> And there were special handling to ingore swap-cache page. But, shmem can
> be swap-cache and file-cache at the same time. Chekcing PageSwapCache() is
> not correct here. Check PageAnon() instead.

When/How shmem can be both swap-cache and file-cache ?
I can't understand that situation.

Thanks. :)

> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Acked-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>
> ---
>  mm/migrate.c |   11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> Index: b/mm/migrate.c
> ===================================================================
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -332,7 +332,13 @@ static int migrate_page_move_mapping(str
>        __inc_zone_page_state(newpage, NR_FILE_PAGES);
>
>        spin_unlock_irq(&mapping->tree_lock);
> -       if (!PageSwapCache(newpage))
> +
> +       /*
> +        * The page is removed from radix-tree implicitly.
> +        * We uncharge it here but swap cache of anonymous page should be
> +        * uncharged by mem_cgroup_ucharge_page().
> +        */
> +       if (!PageAnon(newpage))
>                mem_cgroup_uncharge_cache_page(page);
>
>        return 0;
> @@ -381,7 +387,8 @@ static void migrate_page_copy(struct pag
>                /*
>                 * SwapCache is removed implicitly. Uncharge against swapcache
>                 * should be called after ClearPageSwapCache() because
> -                * mem_cgroup_uncharge_page checks the flag.
> +                * mem_cgroup_uncharge_page checks the flag. shmem's swap cache
> +                * is uncharged before here.
>                 */
>                mem_cgroup_uncharge_page(page);
>        }
>
>
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-- 
Kinds regards,
MinChan Kim
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