It is observed that sometimes multiple tasks get blocked for long
in the congestion_wait loop below, in shrink_inactive_list. This
is because of vm_stat values not being synced.
(__schedule) from [<c0a03328>]
(schedule_timeout) from [<c0a04940>]
(io_schedule_timeout) from [<c01d585c>]
(congestion_wait) from [<c01cc9d8>]
(shrink_inactive_list) from [<c01cd034>]
(shrink_zone) from [<c01cdd08>]
(try_to_free_pages) from [<c01c442c>]
(__alloc_pages_nodemask) from [<c01f1884>]
(new_slab) from [<c09fcf60>]
(__slab_alloc) from [<c01f1a6c>]
In one such instance, zone_page_state(zone, NR_ISOLATED_FILE)
had returned 14, zone_page_state(zone, NR_INACTIVE_FILE)
returned 92, and GFP_IOFS was set, and this resulted
in too_many_isolated returning true. But one of the CPU's
pageset vm_stat_diff had NR_ISOLATED_FILE as "-14". So the
actual isolated count was zero. As there weren't any more
updates to NR_ISOLATED_FILE and vmstat_update deffered work
had not been scheduled yet, 7 tasks were spinning in the
congestion wait loop for around 4 seconds, in the direct
reclaim path.
This patch uses zone_page_state_snapshot instead, but restricts
its usage to avoid performance penalty.
Signed-off-by: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
---
mm/vmscan.c | 56 +++++++++++++++++++++++++++++++++++++-------------------
1 file changed, 37 insertions(+), 19 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5e8772b..266551f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1392,6 +1392,32 @@ int isolate_lru_page(struct page *page)
return ret;
}
+static int __too_many_isolated(struct zone *zone, int file,
+ struct scan_control *sc, int safe)
+{
+ unsigned long inactive, isolated;
+
+ if (safe) {
+ inactive = zone_page_state_snapshot(zone,
+ NR_INACTIVE_ANON + 2 * file);
+ isolated = zone_page_state_snapshot(zone,
+ NR_ISOLATED_ANON + file);
+ } else {
+ inactive = zone_page_state(zone, NR_INACTIVE_ANON + 2 * file);
+ isolated = zone_page_state(zone, NR_ISOLATED_ANON + file);
+ }
+
+ /*
+ * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
+ * won't get blocked by normal direct-reclaimers, forming a circular
+ * deadlock.
+ */
+ if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
+ inactive >>= 3;
+
+ return isolated > inactive;
+}
+
/*
* A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
* then get resheduled. When there are massive number of tasks doing page
@@ -1400,33 +1426,22 @@ int isolate_lru_page(struct page *page)
* unnecessary swapping, thrashing and OOM.
*/
static int too_many_isolated(struct zone *zone, int file,
- struct scan_control *sc)
+ struct scan_control *sc, int safe)
{
- unsigned long inactive, isolated;
-
if (current_is_kswapd())
return 0;
if (!global_reclaim(sc))
return 0;
- if (file) {
- inactive = zone_page_state(zone, NR_INACTIVE_FILE);
- isolated = zone_page_state(zone, NR_ISOLATED_FILE);
- } else {
- inactive = zone_page_state(zone, NR_INACTIVE_ANON);
- isolated = zone_page_state(zone, NR_ISOLATED_ANON);
+ if (unlikely(__too_many_isolated(zone, file, sc, 0))) {
+ if (safe)
+ return __too_many_isolated(zone, file, sc, safe);
+ else
+ return 1;
}
- /*
- * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
- * won't get blocked by normal direct-reclaimers, forming a circular
- * deadlock.
- */
- if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
- inactive >>= 3;
-
- return isolated > inactive;
+ return 0;
}
static noinline_for_stack void
@@ -1516,15 +1531,18 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
unsigned long nr_immediate = 0;
isolate_mode_t isolate_mode = 0;
int file = is_file_lru(lru);
+ int safe = 0;
struct zone *zone = lruvec_zone(lruvec);
struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
- while (unlikely(too_many_isolated(zone, file, sc))) {
+ while (unlikely(too_many_isolated(zone, file, sc, safe))) {
congestion_wait(BLK_RW_ASYNC, HZ/10);
/* We are about to die and free our memory. Return now. */
if (fatal_signal_pending(current))
return SWAP_CLUSTER_MAX;
+
+ safe = 1;
}
lru_add_drain();
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