[PATCH] zone_reclaim: additional comments and cleanup
Add some comments to explain how zone reclaim works. And it fixes the
following issues:
- PF_SWAPWRITE needs to be set for RECLAIM_SWAP to be able to write
out pages to swap. Currently RECLAIM_SWAP may not do that.
- remove setting nr_reclaimed pages after slab reclaim since the slab shrinking
code does not use that and the nr_reclaimed pages is just right for the
intended follow up action.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2d5d486..c712b94 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1887,6 +1887,7 @@
*/
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
+ /* Minimum pages needed in order to stay on node */
const unsigned long nr_pages = 1 << order;
struct task_struct *p = current;
struct reclaim_state reclaim_state;
@@ -1924,9 +1925,12 @@
if (nr_reclaimed < nr_pages && (zone_reclaim_mode & RECLAIM_SLAB)) {
/*
- * shrink_slab does not currently allow us to determine
- * how many pages were freed in the zone. So we just
- * shake the slab and then go offnode for a single allocation.
+ * shrink_slab() does not currently allow us to determine how
+ * many pages were freed in this zone. So we just shake the slab
+ * a bit and then go off node for this particular allocation
+ * despite possibly having freed enough memory to allocate in
+ * this zone. If we freed local memory then the next
+ * allocations will be local again.
*
* shrink_slab will free memory on all zones and may take
* a long time.
@@ -1937,8 +1941,14 @@
p->reclaim_state = NULL;
current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
- if (nr_reclaimed == 0)
+ if (nr_reclaimed == 0) {
+ /*
+ * We were unable to reclaim enough pages to stay on node. We
+ * now allow off node accesses for a certain time period before
+ * trying again to reclaim pages from the local zone.
+ */
zone->last_unsuccessful_zone_reclaim = jiffies;
+ }
return nr_reclaimed >= nr_pages;
}