Page reclaim determines whether a pgdat is unreclaimable by examining how
many pages have been scanned since a page was freed and comparing that to
the LRU sizes. Skipped pages are not reclaim candidates but contribute to
scanned. This can prematurely mark a pgdat as unreclaimable and trigger
an OOM kill.
This patch accounts for skipped pages as a partial scan so that an
unreclaimable pgdat will still be marked as such but by scaling the cost
of a skip, it'll avoid the pgdat being marked prematurely.
Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
---
mm/vmscan.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6810d81f60c7..e5af357dd4ac 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1424,7 +1424,7 @@ static unsigned long isolate_lru_pages(unsigned long
nr_to_scan,
LIST_HEAD(pages_skipped);
for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
- !list_empty(src); scan++) {
+ !list_empty(src);) {
struct page *page;
page = lru_to_page(src);
@@ -1438,6 +1438,12 @@ static unsigned long isolate_lru_pages(unsigned long
nr_to_scan,
continue;
}
+ /*
+ * Account for scanned and skipped separetly to avoid the pgdat
+ * being prematurely marked unreclaimable by pgdat_reclaimable.
+ */
+ scan++;
+
switch (__isolate_lru_page(page, mode)) {
case 0:
nr_pages = hpage_nr_pages(page);
@@ -1465,14 +1471,24 @@ static unsigned long isolate_lru_pages(unsigned long
nr_to_scan,
*/
if (!list_empty(&pages_skipped)) {
int zid;
+ unsigned long total_skipped = 0;
- list_splice(&pages_skipped, src);
for (zid = 0; zid < MAX_NR_ZONES; zid++) {
if (!nr_skipped[zid])
continue;
__count_zid_vm_events(PGSCAN_SKIP, zid,
nr_skipped[zid]);
+ total_skipped += nr_skipped[zid];
}
+
+ /*
+ * Account skipped pages as a partial scan as the pgdat may be
+ * close to unreclaimable. If the LRU list is empty, account
+ * skipped pages as a full scan.
+ */
+ scan += list_empty(src) ? total_skipped : total_skipped >> 2;
+
+ list_splice(&pages_skipped, src);
}
*nr_scanned = scan;
trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
scan,
--
2.6.4
