On Thu, 8 Jul 2010 16:38:10 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
> 'slab_reclaimable' and 'nr_pages' are unsigned. so, subtraction is
> unsafe.
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Acked-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
> ---
> mm/vmscan.c | 14 +++++++-------
> 1 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9c7e57c..8715da1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2588,7 +2588,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> .swappiness = vm_swappiness,
> .order = order,
> };
> - unsigned long slab_reclaimable;
> + unsigned long n, m;
Please use better identifiers.
> disable_swap_token();
> cond_resched();
> @@ -2615,8 +2615,8 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
> }
>
> - slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
> - if (slab_reclaimable > zone->min_slab_pages) {
> + n = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
> + if (n > zone->min_slab_pages) {
> /*
> * shrink_slab() does not currently allow us to determine how
> * many pages were freed in this zone. So we take the current
> @@ -2628,16 +2628,16 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> * take a long time.
> */
> while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
> - zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
> - slab_reclaimable - nr_pages)
> + (zone_page_state(zone, NR_SLAB_RECLAIMABLE) + nr_pages > n))
> ;
>
> /*
> * Update nr_reclaimed by the number of slab pages we
> * reclaimed from this zone.
> */
> - sc.nr_reclaimed += slab_reclaimable -
> - zone_page_state(zone, NR_SLAB_RECLAIMABLE);
> + m = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
> + if (m < n)
> + sc.nr_reclaimed += n - m;
And it's not a completly trivial objection. Your patch made the above
code snippet quite a lot harder to read (and hence harder to maintain).
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