linux-kernel - Re: [PATCH 1/2] mm/vmscan: restore sc->gfp_mask after promoting it to __GFP

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Date:	Thu, 13 Feb 2014 11:10:28 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Weijie Yang <weijie.yang@...sung.com>,
	"'Mel Gorman'" <mgorman@...e.de>
CC:	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	"'Minchan Kim'" <minchan@...nel.org>, weijie.yang.kh@...il.com,
	"'Linux-MM'" <linux-mm@...ck.org>,
	"'linux-kernel'" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm/vmscan: restore sc->gfp_mask after promoting it
 to __GFP_HIGHMEM

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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