On 02/12/2014 09:39 PM, Weijie Yang wrote:

> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2298,14 +2298,17 @@ static bool shrink_zones(struct zonelist *zonelist, 
> struct scan_control *sc)
>       unsigned long nr_soft_reclaimed;
>       unsigned long nr_soft_scanned;
>       bool aborted_reclaim = false;
> +     bool promoted_mask = false;
>  
>       /*
>        * If the number of buffer_heads in the machine exceeds the maximum
>        * allowed level, force direct reclaim to scan the highmem zone as
>        * highmem pages could be pinning lowmem pages storing buffer_heads
>        */
> -     if (buffer_heads_over_limit)
> +     if (buffer_heads_over_limit) {

It took me a minute to figure out why you are doing things this way,
so maybe this could use a comment, or maybe it could be done in a
simpler way, by simply saving and restoring the original mask?

                orig_mask = sc->gfp_mask;

> +             promoted_mask = !(sc->gfp_mask & __GFP_HIGHMEM);
>               sc->gfp_mask |= __GFP_HIGHMEM;
> +     }
>  
>       for_each_zone_zonelist_nodemask(zone, z, zonelist,
>                                       gfp_zone(sc->gfp_mask), sc->nodemask) {
> @@ -2354,6 +2357,9 @@ static bool shrink_zones(struct zonelist *zonelist, 
> struct scan_control *sc)
>               shrink_zone(zone, sc);
>       }
>  
> +     if (promoted_mask)
                sc->gfp_mask = orig_mask;

> +             sc->gfp_mask &= ~__GFP_HIGHMEM;
> +
>       return aborted_reclaim;
>  }
>  
> 


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