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-rw-r--r--mm/mmzone.c21
-rw-r--r--mm/page_alloc.c4
-rw-r--r--mm/vmstat.c15
3 files changed, 37 insertions, 3 deletions
diff --git a/mm/mmzone.c b/mm/mmzone.c
index f5b7d17..e35bfb8 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -87,3 +87,24 @@ int memmap_valid_within(unsigned long pfn,
return 1;
}
#endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
+
+#ifdef CONFIG_SMP
+/* Called when a more accurate view of NR_FREE_PAGES is needed */
+unsigned long zone_nr_free_pages(struct zone *zone)
+{
+ unsigned long nr_free_pages = zone_page_state(zone, NR_FREE_PAGES);
+
+ /*
+ * While kswapd is awake, it is considered the zone is under some
+ * memory pressure. Under pressure, there is a risk that
+ * per-cpu-counter-drift will allow the min watermark to be breached
+ * potentially causing a live-lock. While kswapd is awake and
+ * free pages are low, get a better estimate for free pages
+ */
+ if (nr_free_pages < zone->percpu_drift_mark &&
+ !waitqueue_active(&zone->zone_pgdat->kswapd_wait))
+ return zone_page_state_snapshot(zone, NR_FREE_PAGES);
+
+ return nr_free_pages;
+}
+#endif /* CONFIG_SMP */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 452e2ba0..b2d21e0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1462,7 +1462,7 @@ int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
{
/* free_pages my go negative - that's OK */
long min = mark;
- long free_pages = zone_page_state(z, NR_FREE_PAGES) - (1 << order) + 1;
+ long free_pages = zone_nr_free_pages(z) - (1 << order) + 1;
int o;
if (alloc_flags & ALLOC_HIGH)
@@ -2424,7 +2424,7 @@ void show_free_areas(void)
" all_unreclaimable? %s"
"\n",
zone->name,
- K(zone_page_state(zone, NR_FREE_PAGES)),
+ K(zone_nr_free_pages(zone)),
K(min_wmark_pages(zone)),
K(low_wmark_pages(zone)),
K(high_wmark_pages(zone)),
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a8d6b59..355a9e6 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -138,11 +138,24 @@ static void refresh_zone_stat_thresholds(void)
int threshold;
for_each_populated_zone(zone) {
+ unsigned long max_drift, tolerate_drift;
+
threshold = calculate_threshold(zone);
for_each_online_cpu(cpu)
per_cpu_ptr(zone->pageset, cpu)->stat_threshold
= threshold;
+
+ /*
+ * Only set percpu_drift_mark if there is a danger that
+ * NR_FREE_PAGES reports the low watermark is ok when in fact
+ * the min watermark could be breached by an allocation
+ */
+ tolerate_drift = low_wmark_pages(zone) - min_wmark_pages(zone);
+ max_drift = num_online_cpus() * threshold;
+ if (max_drift > tolerate_drift)
+ zone->percpu_drift_mark = high_wmark_pages(zone) +
+ max_drift;
}
}
@@ -813,7 +826,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
"\n scanned %lu"
"\n spanned %lu"
"\n present %lu",
- zone_page_state(zone, NR_FREE_PAGES),
+ zone_nr_free_pages(zone),
min_wmark_pages(zone),
low_wmark_pages(zone),
high_wmark_pages(zone),
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