Commit b15e0905 authored by akpm@osdl.org's avatar akpm@osdl.org Committed by Linus Torvalds
Browse files

[PATCH] vmscan: notice slab shrinking 



Fix a problem identified by Andrea Arcangeli <andrea@suse.de>

kswapd will set a zone into all_unreclaimable state if it sees that we're not
successfully reclaiming LRU pages.  But that fails to notice that we're
successfully reclaiming slab obects, so we can set all_unreclaimable too soon.

So change shrink_slab() to return a success indication if it actually
reclaimed some objects, and don't assume that the zone is all_unreclaimable if
that is true.  This means that we won't enter all_unreclaimable state if we
are successfully freeing slab objects but we're not yet actually freeing slab
pages, due to internal fragmentation.

(hm, this has a shortcoming.  We could be successfully freeing ZONE_NORMAL
slab objects while being really oom on ZONE_DMA.  If that happens then kswapd
might burn a lot of CPU.  But given that there might be some slab objects in
ZONE_DMA, perhaps that is appropriate.)

Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 39c715b7

mm/vmscan.c

+14 −5
Original line number Diff line number Diff line
@@ -180,17 +180,20 @@ EXPORT_SYMBOL(remove_shrinker); 
 * `lru_pages' represents the number of on-LRU pages in all the zones which

 * are eligible for the caller's allocation attempt.  It is used for balancing

 * slab reclaim versus page reclaim.

 *

 * Returns the number of slab objects which we shrunk.

 */

static int shrink_slab(unsigned long scanned, unsigned int gfp_mask,

			unsigned long lru_pages)

{

	struct shrinker *shrinker;

	int ret = 0;



	if (scanned == 0)

		scanned = SWAP_CLUSTER_MAX;



	if (!down_read_trylock(&shrinker_rwsem))

		return 0;

		return 1;	/* Assume we'll be able to shrink next time */



	list_for_each_entry(shrinker, &shrinker_list, list) {

		unsigned long long delta;
@@ -209,10 +212,14 @@ static int shrink_slab(unsigned long scanned, unsigned int gfp_mask, 
		while (total_scan >= SHRINK_BATCH) {

			long this_scan = SHRINK_BATCH;

			int shrink_ret;

			int nr_before;



			nr_before = (*shrinker->shrinker)(0, gfp_mask);

			shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);

			if (shrink_ret == -1)

				break;

			if (shrink_ret < nr_before)

				ret += nr_before - shrink_ret;

			mod_page_state(slabs_scanned, this_scan);

			total_scan -= this_scan;
@@ -222,7 +229,7 @@ static int shrink_slab(unsigned long scanned, unsigned int gfp_mask, 
		shrinker->nr += total_scan;

	}

	up_read(&shrinker_rwsem);

	return 0;

	return ret;

}



/* Called without lock on whether page is mapped, so answer is unstable */
@@ -1079,6 +1086,7 @@ scan: 
		 */

		for (i = 0; i <= end_zone; i++) {

			struct zone *zone = pgdat->node_zones + i;

			int nr_slab;



			if (zone->present_pages == 0)

				continue;
@@ -1100,14 +1108,15 @@ scan: 
			sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;

			shrink_zone(zone, &sc);

			reclaim_state->reclaimed_slab = 0;

			shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);

			nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,

						lru_pages);

			sc.nr_reclaimed += reclaim_state->reclaimed_slab;

			total_reclaimed += sc.nr_reclaimed;

			total_scanned += sc.nr_scanned;

			if (zone->all_unreclaimable)

				continue;

			if (zone->pages_scanned >= (zone->nr_active +

							zone->nr_inactive) * 4)

			if (nr_slab == 0 && zone->pages_scanned >=

				    (zone->nr_active + zone->nr_inactive) * 4)

				zone->all_unreclaimable = 1;

			/*

			 * If we've done a decent amount of scanning and

CRA Git | Maintained and supported by SUSTech CRA and CCSE