Fix a problem identified by Andrea Arcangeli 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 is wrong. 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: Andrew Morton --- 25-akpm/mm/vmscan.c | 19 ++++++++++++++----- 1 files changed, 14 insertions(+), 5 deletions(-) diff -puN mm/vmscan.c~vmscan-notice-slab-shrinking mm/vmscan.c --- 25/mm/vmscan.c~vmscan-notice-slab-shrinking 2005-03-16 21:41:48.000000000 -0800 +++ 25-akpm/mm/vmscan.c 2005-03-16 21:41:48.000000000 -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 */ @@ -1082,6 +1089,7 @@ scan: */ for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; + int nr_slab; if (zone->present_pages == 0) continue; @@ -1103,14 +1111,15 @@ 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 _