1 files changed, 32 insertions, 9 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8d4335779633..eaaef2a09424 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4035,12 +4035,37 @@ static int __meminit zone_batchsize(struct zone *zone)
 #endif
 }
 
+/*
+ * pcp->high and pcp->batch values are related and dependent on one another:
+ * ->batch must never be higher then ->high.
+ * The following function updates them in a safe manner without read side
+ * locking.
+ *
+ * Any new users of pcp->batch and pcp->high should ensure they can cope with
+ * those fields changing asynchronously (acording the the above rule).
+ *
+ * mutex_is_locked(&pcp_batch_high_lock) required when calling this function
+ * outside of boot time (or some other assurance that no concurrent updaters
+ * exist).
+ */
+static void pageset_update(struct per_cpu_pages *pcp, unsigned long high,
+                unsigned long batch)
+{
+       /* start with a fail safe value for batch */
+        pcp->batch = 1;
+        smp_wmb();
+
+       /* Update high, then batch, in order */
+        pcp->high = high;
+        smp_wmb();
+
+        pcp->batch = batch;
+}
+
 /* a companion to setup_pagelist_highmark() */
 static void pageset_set_batch(struct per_cpu_pageset *p, unsigned long batch)
 {
-        struct per_cpu_pages *pcp = &p->pcp;
-        pcp->high = 6 * batch;
-        pcp->batch = max(1UL, 1 * batch);
+        pageset_update(&p->pcp, 6 * batch, max(1UL, 1 * batch));
 }
 
 static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
@@ -4064,13 +4089,11 @@ static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
 static void setup_pagelist_highmark(struct per_cpu_pageset *p,
                                 unsigned long high)
 {
-        struct per_cpu_pages *pcp;
+        unsigned long batch = max(1UL, high / 4);
+        if ((high / 4) > (PAGE_SHIFT * 8))
+                batch = PAGE_SHIFT * 8;
 
-        pcp = &p->pcp;
-        pcp->high = high;
-        pcp->batch = max(1UL, high/4);
-        if ((high/4) > (PAGE_SHIFT * 8))
-                pcp->batch = PAGE_SHIFT * 8;
+        pageset_update(&p->pcp, high, batch);
 }
 
 static void __meminit setup_zone_pageset(struct zone *zone)