Re: OOM problems with 2.6.11-rc4

Andrew Morton
2005-03-16T12:17:55Z

Andrew Morton <akpm@osdl.org> wrote:
>
> Still, I think it would make more sense to return a success indication from
> shrink_slab() if we actually freed any slab objects. That will prevent us
> from incorrectly going all_unreclaimable if all we happen to be doing is
> increasing slab internal fragmentation.
>
> We could do that kludgily by re-polling the shrinker but it would be better
> to return a second value from all the shrinkers.

This is the kludgy version.

--- 25/mm/vmscan.c~vmscan-notice-slab-shrinking 2005-03-16 04:12:49.000000000 -0800
+++ 25-akpm/mm/vmscan.c 2005-03-16 04:14:02.000000000 -0800
@@ -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 sca
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 sca
shrinker->nr += total_scan;
}
up_read(&shrinker_rwsem);
- return 0;
+ return ret;
}

/* Called without lock on whether page is mapped, so answer is unstable */
@@ -1077,6 +1084,7 @@ scan:
*/
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
+ int nr_slab;

if (zone->present_pages == 0)
continue;
@@ -1098,14 +1106,15 @@ 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
_