thp: set recommended min free kbytes

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 52 insertions, 0 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7b55fe0e998b..4ed97a2a115f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -85,6 +85,47 @@ 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))
+                return 0;
+
+        for_each_populated_zone(zone)
+                nr_zones++;
+
+        /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
+        recommended_min = pageblock_nr_pages * 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 += pageblock_nr_pages * nr_zones *
+                           MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
+
+        /* 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;
@@ -108,6 +149,8 @@ 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);
@@ -177,6 +220,13 @@ static ssize_t enabled_store(struct kobject *kobj,
                         ret = err;
         }
 
+        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 =
@@ -464,6 +514,8 @@ static int __init hugepage_init(void)
 
         start_khugepaged();
 
+        set_recommended_min_free_kbytes();
+
 out:
         return err;
 }