[PATCH 05 of 13] reduce the probability of an OOM livelock

Andrea Arcangeli
2008-01-08T07:50:36Z

# Date 1199470021 -3600
# Node ID 351a3906181f5c0fe0137b6f066f725bd65673ba
# Parent e08fdb8dad51268d7a786625fc54c65f277f736b
reduce the probability of an OOM livelock

There's no need to loop way too many times over the lrus in order to
declare defeat and decide to kill a task. The more loops we do the more
likely there we'll run in a livelock with a page bouncing back and
forth between tasks. The maximum number of entries to check in a loop
that returns less than swap-cluster-max pages freed, should be the size
of the list (or at most twice the size of the list if you want to be
really paranoid about the PG_referenced bit).

Our objective there is to know reliably when it's time that we kill a
task, tring to free a few more pages at that already ciritical point is
worthless.

This seems to have the effect of reducing the "hang" time during oom
killing.

Signed-off-by: Andrea Arcangeli <andrea@suse.de>

diff --git a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1211,7 +1211,6 @@ unsigned long try_to_free_pages(struct z
int priority;
int ret = 0;
unsigned long total_scanned = 0;
- unsigned long nr_reclaimed = 0;
struct reclaim_state *reclaim_state = current->reclaim_state;
unsigned long lru_pages = 0;
int i;
@@ -1237,15 +1236,17 @@ unsigned long try_to_free_pages(struct z
}

for (priority = DEF_PRIORITY; priority >= 0; priority--) {
+ unsigned long nr_reclaimed;
+
sc.nr_scanned = 0;
if (!priority)
disable_swap_token();
- nr_reclaimed += shrink_zones(priority, zones, &sc);
+ nr_reclaimed = shrink_zones(priority, zones, &sc);
+ if (reclaim_state)
+ reclaim_state->reclaimed_slab = 0;
shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
- if (reclaim_state) {
+ if (reclaim_state)
nr_reclaimed += reclaim_state->reclaimed_slab;
- reclaim_state->reclaimed_slab = 0;
- }
total_scanned += sc.nr_scanned;
if (nr_reclaimed >= sc.swap_cluster_max) {
ret = 1;
@@ -1320,7 +1321,6 @@ static unsigned long balance_pgdat(pg_da
int priority;
int i;
unsigned long total_scanned;
- unsigned long nr_reclaimed;
struct reclaim_state *reclaim_state = current->reclaim_state;
struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
@@ -1337,7 +1337,6 @@ static unsigned long balance_pgdat(pg_da

loop_again:
total_scanned = 0;
- nr_reclaimed = 0;
sc.may_writepage = !laptop_mode;
count_vm_event(PAGEOUTRUN);

@@ -1347,6 +1346,7 @@ loop_again:
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long lru_pages = 0;
+ unsigned long nr_reclaimed;

/* The swap token gets in the way of swapout... */
if (!priority)
@@ -1393,6 +1393,7 @@ loop_again:
* pages behind kswapd's direction of progress, which would
* cause too much scanning of the lower zones.
*/
+ nr_reclaimed = 0;
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
int nr_slab;