2 files changed, 57 insertions, 6 deletions

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 435e5f794b3b..b06a30fbedff 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -13,6 +13,7 @@
 #include <linux/memory.h>
 #include <linux/notifier.h>
 #include <linux/sched.h>
+#include <linux/mman.h>
 #include "internal.h"
 
 #ifdef CONFIG_DEBUG_MEMORY_INIT
@@ -144,14 +145,23 @@ EXPORT_SYMBOL_GPL(mm_kobj);
 #ifdef CONFIG_SMP
 s32 vm_committed_as_batch = 32;
 
-static void __meminit mm_compute_batch(void)
+void mm_compute_batch(int overcommit_policy)
 {
 	u64 memsized_batch;
 	s32 nr = num_present_cpus();
 	s32 batch = max_t(s32, nr*2, 32);
-
-	/* batch size set to 0.4% of (total memory/#cpus), or max int32 */
-	memsized_batch = min_t(u64, (totalram_pages()/nr)/256, 0x7fffffff);
+	unsigned long ram_pages = totalram_pages();
+
+	/*
+	 * For policy OVERCOMMIT_NEVER, set batch size to 0.4% of
+	 * (total memory/#cpus), and lift it to 25% for other policies
+	 * to easy the possible lock contention for percpu_counter
+	 * vm_committed_as, while the max limit is INT_MAX
+	 */
+	if (overcommit_policy == OVERCOMMIT_NEVER)
+		memsized_batch = min_t(u64, ram_pages/nr/256, INT_MAX);
+	else
+		memsized_batch = min_t(u64, ram_pages/nr/4, INT_MAX);
 
 	vm_committed_as_batch = max_t(s32, memsized_batch, batch);
 }
@@ -162,7 +172,7 @@ static int __meminit mm_compute_batch_notifier(struct notifier_block *self,
 	switch (action) {
 	case MEM_ONLINE:
 	case MEM_OFFLINE:
-		mm_compute_batch();
+		mm_compute_batch(sysctl_overcommit_memory);
 	default:
 		break;
 	}
@@ -176,7 +186,7 @@ static struct notifier_block compute_batch_nb __meminitdata = {
 
 static int __init mm_compute_batch_init(void)
 {
-	mm_compute_batch();
+	mm_compute_batch(sysctl_overcommit_memory);
 	register_hotmemory_notifier(&compute_batch_nb);
 
 	return 0;
diff --git a/mm/util.c b/mm/util.c
index 1c9d097d7e48..8d6280c05238 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -746,6 +746,47 @@ int overcommit_ratio_handler(struct ctl_table *table, int write, void *buffer,
 	return ret;
 }
 
+static void sync_overcommit_as(struct work_struct *dummy)
+{
+	percpu_counter_sync(&vm_committed_as);
+}
+
+int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
+		size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table t;
+	int new_policy;
+	int ret;
+
+	/*
+	 * The deviation of sync_overcommit_as could be big with loose policy
+	 * like OVERCOMMIT_ALWAYS/OVERCOMMIT_GUESS. When changing policy to
+	 * strict OVERCOMMIT_NEVER, we need to reduce the deviation to comply
+	 * with the strict "NEVER", and to avoid possible race condtion (even
+	 * though user usually won't too frequently do the switching to policy
+	 * OVERCOMMIT_NEVER), the switch is done in the following order:
+	 *	1. changing the batch
+	 *	2. sync percpu count on each CPU
+	 *	3. switch the policy
+	 */
+	if (write) {
+		t = *table;
+		t.data = &new_policy;
+		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
+		if (ret)
+			return ret;
+
+		mm_compute_batch(new_policy);
+		if (new_policy == OVERCOMMIT_NEVER)
+			schedule_on_each_cpu(sync_overcommit_as);
+		sysctl_overcommit_memory = new_policy;
+	} else {
+		ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	}
+
+	return ret;
+}
+
 int overcommit_kbytes_handler(struct ctl_table *table, int write, void *buffer,
 		size_t *lenp, loff_t *ppos)
 {