Re: [PATCH 2/2] mm: fix declarations of nr, delta and nr_pagecache_reclaimable

Andrew Morton
2015-09-29T23:07:31Z

On Sun, 27 Sep 2015 21:04:25 +0000 Alexandru Moise <00moses.alexander00@gmail.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;
_