1 files changed, 29 insertions, 1 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 70aa951ecb3c..2e9a2036c114 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -952,6 +952,7 @@ struct ext4_sb_info {
         atomic_t s_mb_lost_chunks;
         atomic_t s_mb_preallocated;
         atomic_t s_mb_discarded;
+        atomic_t s_lock_busy;
 
         /* locality groups */
         struct ext4_locality_group *s_locality_groups;
@@ -1593,15 +1594,42 @@ struct ext4_group_info {
 #define EXT4_MB_GRP_NEED_INIT(grp)      \
         (test_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &((grp)->bb_state)))
 
+#define EXT4_MAX_CONTENTION             8
+#define EXT4_CONTENTION_THRESHOLD       2
+
 static inline spinlock_t *ext4_group_lock_ptr(struct super_block *sb,
                                               ext4_group_t group)
 {
         return bgl_lock_ptr(EXT4_SB(sb)->s_blockgroup_lock, group);
 }
 
+/*
+ * Returns true if the filesystem is busy enough that attempts to
+ * access the block group locks has run into contention.
+ */
+static inline int ext4_fs_is_busy(struct ext4_sb_info *sbi)
+{
+        return (atomic_read(&sbi->s_lock_busy) > EXT4_CONTENTION_THRESHOLD);
+}
+
 static inline void ext4_lock_group(struct super_block *sb, ext4_group_t group)
 {
-        spin_lock(ext4_group_lock_ptr(sb, group));
+        spinlock_t *lock = ext4_group_lock_ptr(sb, group);
+        if (spin_trylock(lock))
+                /*
+                 * We're able to grab the lock right away, so drop the
+                 * lock contention counter.
+                 */
+                atomic_add_unless(&EXT4_SB(sb)->s_lock_busy, -1, 0);
+        else {
+                /*
+                 * The lock is busy, so bump the contention counter,
+                 * and then wait on the spin lock.
+                 */
+                atomic_add_unless(&EXT4_SB(sb)->s_lock_busy, 1,
+                                  EXT4_MAX_CONTENTION);
+                spin_lock(lock);
+        }
 }
 
 static inline void ext4_unlock_group(struct super_block *sb,