Subject: set recommended min free kbytes

From: Andrea Arcangeli <aarcange@redhat.com>

If transparent hugepage is enabled initialize min_free_kbytes to an optimal
value by default. This moves the hugeadm algorithm in kernel.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -86,6 +86,51 @@ struct khugepaged_scan {
 	.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 };
 
+
+static int set_recommended_min_free_kbytes(void)
+{
+	struct zone *zone;
+	int nr_zones = 0;
+	unsigned long recommended_min;
+	extern int min_free_kbytes;
+
+	if (!test_bit(TRANSPARENT_HUGEPAGE_FLAG,
+		      &transparent_hugepage_flags) &&
+	    !test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
+		      &transparent_hugepage_flags) &&
+	    !test_bit(TRANSPARENT_HUGEPAGE_KHUGEPAGED_FLAG,
+		      &transparent_hugepage_flags) &&
+	    !test_bit(TRANSPARENT_HUGEPAGE_KHUGEPAGED_REQ_MADV_FLAG,
+		      &transparent_hugepage_flags))
+		return 0;
+
+	for_each_populated_zone(zone)
+		nr_zones++;
+
+	/* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
+	recommended_min = HPAGE_PMD_NR * nr_zones * 2;
+
+	/*
+	 * Make sure that on average at least two pageblocks are almost free
+	 * of another type, one for a migratetype to fall back to and a
+	 * second to avoid subsequent fallbacks of other types There are 3
+	 * MIGRATE_TYPES we care about.
+	 */
+	recommended_min += HPAGE_PMD_NR * nr_zones * 3 * 3;
+
+	/* don't ever allow to reserve more than 5% of the lowmem */
+	recommended_min = min(recommended_min,
+			      (unsigned long) nr_free_buffer_pages() / 20);
+	recommended_min <<= (PAGE_SHIFT-10);
+
+	if (recommended_min > min_free_kbytes) {
+		min_free_kbytes = recommended_min;
+		setup_per_zone_wmarks();
+	}
+	return 0;
+}
+late_initcall(set_recommended_min_free_kbytes);
+
 static int start_khugepaged(void)
 {
 	int err = 0;
@@ -113,6 +158,8 @@ static int start_khugepaged(void)
 		mutex_unlock(&khugepaged_mutex);
 		if (wakeup)
 			wake_up_interruptible(&khugepaged_wait);
+
+		set_recommended_min_free_kbytes();
 	} else
 		/* wakeup to exit */
 		wake_up_interruptible(&khugepaged_wait);
@@ -178,9 +225,20 @@ static ssize_t enabled_store(struct kobj
 			     struct kobj_attribute *attr,
 			     const char *buf, size_t count)
 {
-	return double_flag_store(kobj, attr, buf, count,
-				 TRANSPARENT_HUGEPAGE_FLAG,
-				 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
+	ssize_t ret;
+
+	ret = double_flag_store(kobj, attr, buf, count,
+				TRANSPARENT_HUGEPAGE_FLAG,
+				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
+
+	if (ret > 0 &&
+	    (test_bit(TRANSPARENT_HUGEPAGE_FLAG,
+		      &transparent_hugepage_flags) ||
+	     test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
+		      &transparent_hugepage_flags)))
+		set_recommended_min_free_kbytes();
+
+	return ret;
 }
 static struct kobj_attribute enabled_attr =
 	__ATTR(enabled, 0644, enabled_show, enabled_store);
@@ -495,6 +553,8 @@ static int __init hugepage_init(void)
 
 	start_khugepaged();
 
+	set_recommended_min_free_kbytes();
+
 out:
 	return err;
 }