From: Nick Piggin <nickpiggin@yahoo.com.au>
If the zone has a very small number of inactive pages, local variable
`ratio' can be huge and we do way too much scanning. So much so that Ingo
hit an NMI watchdog expiry, although that was because the zone would have a
had a single refcount-zero page in it, and that logic recently got fixed up
via get_page_testone().
Nick's patch simply puts a sane-looking upper bound on the number of pages
which we'll scan in this round. It hasn't had a lot of thought or testing
yet.
---
25-akpm/mm/vmscan.c | 28 +++++++++++++++++++---------
1 files changed, 19 insertions(+), 9 deletions(-)
diff -puN mm/vmscan.c~vm-shrink-zone mm/vmscan.c
--- 25/mm/vmscan.c~vm-shrink-zone Tue May 18 15:06:27 2004
+++ 25-akpm/mm/vmscan.c Tue May 18 15:06:27 2004
@@ -742,23 +742,33 @@ static int
shrink_zone(struct zone *zone, int max_scan, unsigned int gfp_mask,
int *total_scanned, struct page_state *ps, int do_writepage)
{
- unsigned long ratio;
+ unsigned long scan_active;
int count;
/*
* Try to keep the active list 2/3 of the size of the cache. And
* make sure that refill_inactive is given a decent number of pages.
*
- * The "ratio+1" here is important. With pagecache-intensive workloads
- * the inactive list is huge, and `ratio' evaluates to zero all the
- * time. Which pins the active list memory. So we add one to `ratio'
- * just to make sure that the kernel will slowly sift through the
- * active list.
+ * The "scan_active + 1" here is important. With pagecache-intensive
+ * workloads the inactive list is huge, and `ratio' evaluates to zero
+ * all the time. Which pins the active list memory. So we add one to
+ * `scan_active' just to make sure that the kernel will slowly sift
+ * through the active list.
*/
- ratio = (unsigned long)SWAP_CLUSTER_MAX * zone->nr_active /
- ((zone->nr_inactive | 1) * 2);
+ if (zone->nr_active >= 4*(zone->nr_inactive*2 + 1)) {
+ /* Don't scan more than 4 times the inactive list scan size */
+ scan_active = 4*max_scan;
+ } else {
+ unsigned long long tmp;
- atomic_add(ratio+1, &zone->nr_scan_active);
+ /* Cast to long long so the multiply doesn't overflow */
+
+ tmp = (unsigned long long)max_scan * zone->nr_active;
+ do_div(tmp, zone->nr_inactive*2 + 1);
+ scan_active = (unsigned long)tmp;
+ }
+
+ atomic_add(scan_active + 1, &zone->nr_scan_active);
count = atomic_read(&zone->nr_scan_active);
if (count >= SWAP_CLUSTER_MAX) {
atomic_set(&zone->nr_scan_active, 0);
_