Re: [PATCH V5 2/6] mm: don't assume anonymous pages have SwapBacked flag

[Michal Hocko]

On Fri 24-02-17 13:31:45, Shaohua Li wrote:
> There are a few places the code assumes anonymous pages should have
> SwapBacked flag set. MADV_FREE pages are anonymous pages but we are
> going to add them to LRU_INACTIVE_FILE list and clear SwapBacked flag
> for them. The assumption doesn't hold any more, so fix them.
> 
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Shaohua Li <shli@xxxxxx>

Looks good to me.
[...]
> index 96eb85c..c621088 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1416,7 +1416,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  			 * Store the swap location in the pte.
>  			 * See handle_pte_fault() ...
>  			 */
> -			VM_BUG_ON_PAGE(!PageSwapCache(page), page);
> +			VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page),
> +				page);

just this part makes me scratch my head. I really do not understand what
kind of problem it tries to prevent from, maybe I am missing something
obvoious...

>  
>  			if (!PageDirty(page)) {
>  				/* It's a freeable page by MADV_FREE */
> -- 
> 2.9.3
> 

-- 
Michal Hocko
SUSE Labs