Re: [PATCH 1/4] vmscan: change the number of the unmapped files in zone reclaim

Wu Fengguang
2009-05-18T03:16:00Z

On Wed, May 13, 2009 at 12:06:28PM +0900, KOSAKI Motohiro wrote:
> Subject: [PATCH] vmscan: change the number of the unmapped files in zone reclaim
>
> Documentation/sysctl/vm.txt says
>
> A percentage of the total pages in each zone. Zone reclaim will only
> occur if more than this percentage of pages are file backed and unmapped.
> This is to insure that a minimal amount of local pages is still available for
> file I/O even if the node is overallocated.
>
> However, zone_page_state(zone, NR_FILE_PAGES) contain some non file backed pages
> (e.g. swapcache, buffer-head)
>
> The right calculation is to use NR_{IN}ACTIVE_FILE.
>
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Christoph Lameter <cl@linux-foundation.org>
> Cc: Rik van Riel <riel@redhat.com>
> ---
> mm/vmscan.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> Index: b/mm/vmscan.c
> ===================================================================
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2397,6 +2397,7 @@ static int __zone_reclaim(struct zone *z
> .isolate_pages = isolate_pages_global,
> };
> unsigned long slab_reclaimable;
> + long nr_unmapped_file_pages;
>
> disable_swap_token();
> cond_resched();
> @@ -2409,9 +2410,11 @@ static int __zone_reclaim(struct zone *z
> reclaim_state.reclaimed_slab = 0;
> p->reclaim_state = &reclaim_state;
>
> - if (zone_page_state(zone, NR_FILE_PAGES) -
> - zone_page_state(zone, NR_FILE_MAPPED) >
> - zone->min_unmapped_pages) {
> + nr_unmapped_file_pages = zone_page_state(zone, NR_INACTIVE_FILE) +
> + zone_page_state(zone, NR_ACTIVE_FILE) -
> + zone_page_state(zone, NR_FILE_MAPPED);

This can possibly go negative.

> + if (nr_unmapped_file_pages > zone->min_unmapped_pages) {
> /*
> * Free memory by calling shrink zone with increasing
> * priorities until we have enough memory freed.
> @@ -2458,6 +2461,8 @@ int zone_reclaim(struct zone *zone, gfp_
> {
> int node_id;
> int ret;
> + long nr_unmapped_file_pages;
> + long nr_slab_reclaimable;
>
> /*
> * Zone reclaim reclaims unmapped file backed pages and
> @@ -2469,10 +2474,12 @@ int zone_reclaim(struct zone *zone, gfp_
> * if less than a specified percentage of the zone is used by
> * unmapped file backed pages.
> */
> - if (zone_page_state(zone, NR_FILE_PAGES) -
> - zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages
> - && zone_page_state(zone, NR_SLAB_RECLAIMABLE)
> - <= zone->min_slab_pages)
> + nr_unmapped_file_pages = zone_page_state(zone, NR_INACTIVE_FILE) +
> + zone_page_state(zone, NR_ACTIVE_FILE) -
> + zone_page_state(zone, NR_FILE_MAPPED);

Ditto.

Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>

> + nr_slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
> + if (nr_unmapped_file_pages <= zone->min_unmapped_pages &&
> + nr_slab_reclaimable <= zone->min_slab_pages)
> return 0;
>
> if (zone_is_all_unreclaimable(zone))
>
>
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