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-rw-r--r--include/linux/mmzone.h13
-rw-r--r--include/linux/vmstat.h22
-rw-r--r--mm/mmzone.c21
-rw-r--r--mm/page_alloc.c4
-rw-r--r--mm/vmstat.c15
5 files changed, 72 insertions, 3 deletions
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 6e6e62648a4..3984c4eb41f 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -284,6 +284,13 @@ struct zone {
unsigned long watermark[NR_WMARK];
/*
+ * When free pages are below this point, additional steps are taken
+ * when reading the number of free pages to avoid per-cpu counter
+ * drift allowing watermarks to be breached
+ */
+ unsigned long percpu_drift_mark;
+
+ /*
* We don't know if the memory that we're going to allocate will be freeable
* or/and it will be released eventually, so to avoid totally wasting several
* GB of ram we must reserve some of the lower zone memory (otherwise we risk
@@ -441,6 +448,12 @@ static inline int zone_is_oom_locked(const struct zone *zone)
return test_bit(ZONE_OOM_LOCKED, &zone->flags);
}
+#ifdef CONFIG_SMP
+unsigned long zone_nr_free_pages(struct zone *zone);
+#else
+#define zone_nr_free_pages(zone) zone_page_state(zone, NR_FREE_PAGES)
+#endif /* CONFIG_SMP */
+
/*
* The "priority" of VM scanning is how much of the queues we will scan in one
* go. A value of 12 for DEF_PRIORITY implies that we will scan 1/4096th of the
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 7f43ccdc1d3..eaaea37b3b7 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -170,6 +170,28 @@ static inline unsigned long zone_page_state(struct zone *zone,
return x;
}
+/*
+ * More accurate version that also considers the currently pending
+ * deltas. For that we need to loop over all cpus to find the current
+ * deltas. There is no synchronization so the result cannot be
+ * exactly accurate either.
+ */
+static inline unsigned long zone_page_state_snapshot(struct zone *zone,
+ enum zone_stat_item item)
+{
+ long x = atomic_long_read(&zone->vm_stat[item]);
+
+#ifdef CONFIG_SMP
+ int cpu;
+ for_each_online_cpu(cpu)
+ x += per_cpu_ptr(zone->pageset, cpu)->vm_stat_diff[item];
+
+ if (x < 0)
+ x = 0;
+#endif
+ return x;
+}
+
extern unsigned long global_reclaimable_pages(void);
extern unsigned long zone_reclaimable_pages(struct zone *zone);
diff --git a/mm/mmzone.c b/mm/mmzone.c
index f5b7d176021..e35bfb82c85 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 452e2ba06c7..b2d21e06d45 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 a8d6b59e609..355a9e669aa 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),