linux-kernel - Re: [PATCH 2/2] mm: fix declarations of nr, delta and nr_pagecache

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Message-Id: <20150929160727.ef70acf2e44575e9470a4025@linux-foundation.org>
Date:	Tue, 29 Sep 2015 16:07:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alexandru Moise <00moses.alexander00@...il.com>
Cc:	vdavydov@...allels.com, mhocko@...e.cz, hannes@...xchg.org,
	tj@...nel.org, vbabka@...e.cz, mgorman@...e.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: fix declarations of nr, delta and
 nr_pagecache_reclaimable

On Sun, 27 Sep 2015 21:04:25 +0000 Alexandru Moise <00moses.alexander00@...il.com> wrote:

> The nr variable is meant to be returned by a function which is
> declared as returning "unsigned long", so declare nr as such.
> 
> Lower down we should also declare delta and nr_pagecache_reclaimable
> as being unsigned longs because they're used to store the values
> returned by zone_page_state() and zone_unmapped_file_pages() which
> also happen to return unsigned integers.

I rewrote the changelog rather a lot:



Subject: mm/vmscan.c: fix types of some locals

In zone_reclaimable_pages(), `nr' is returned by a function which is
declared as returning "unsigned long", so declare it such.  Negative
values are meaningless here.

In zone_pagecache_reclaimable() we should also declare `delta' and
`nr_pagecache_reclaimable' as being unsigned longs because they're used to
store the values returned by zone_page_state() and
zone_unmapped_file_pages() which also happen to return unsigned integers.



> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -194,7 +194,7 @@ static bool sane_reclaim(struct scan_control *sc)
>  
>  static unsigned long zone_reclaimable_pages(struct zone *zone)
>  {
> -	int nr;
> +	unsigned long nr;
>  
>  	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
>  	     zone_page_state(zone, NR_INACTIVE_FILE);

OK.

> @@ -3698,8 +3698,8 @@ static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
>  /* Work out how many page cache pages we can reclaim in this reclaim_mode */
>  static long zone_pagecache_reclaimable(struct zone *zone)
>  {
> -	long nr_pagecache_reclaimable;
> -	long delta = 0;
> +	unsigned long nr_pagecache_reclaimable;
> +	unsigned long delta = 0;
>  
>  	/*
>  	 * If RECLAIM_UNMAP is set, then all file pages are considered

Also OK, because zone_pagecache_reclaimable() takes care to avoid
returning any negative values.


In fact I believe we should also do this:

--- a/mm/vmscan.c~mm-fix-declarations-of-nr-delta-and-nr_pagecache_reclaimable-fix
+++ a/mm/vmscan.c
@@ -3693,7 +3693,7 @@ static inline unsigned long zone_unmappe
 }
 
 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
-static long zone_pagecache_reclaimable(struct zone *zone)
+static unsigned long zone_pagecache_reclaimable(struct zone *zone)
 {
 	unsigned long nr_pagecache_reclaimable;
 	unsigned long delta = 0;
_

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