Re: [PATCH] mm: vmscan: recompute page status when putting back

[KOSAKI Motohiro]

> If unlikely the given page is isolated from lru list again, its status is
> recomputed before putting back to lru list, since the comment says page's
> status can change while we move it among lru.
>
>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
> ---
>
> --- a/mm/vmscan.c       Thu Dec 29 20:20:16 2011
> +++ b/mm/vmscan.c       Fri Jan  6 21:31:56 2012
> @@ -633,12 +633,14 @@ int remove_mapping(struct address_space
>  void putback_lru_page(struct page *page)
>  {
>        int lru;
> -       int active = !!TestClearPageActive(page);
> -       int was_unevictable = PageUnevictable(page);
> +       int active;
> +       int was_unevictable;
>
>        VM_BUG_ON(PageLRU(page));
>
>  redo:
> +       active = !!TestClearPageActive(page);
> +       was_unevictable = PageUnevictable(page);
>        ClearPageUnevictable(page);

When and How do this race happen?
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