Btrfs: reduce lock contention on extent buffer locks

[sfrench/cifs-2.6.git] / fs / btrfs / extent_io.c

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 3b9fb478b0d1aff2189c713c7e54cfd77a58f885..907ed0025dd4076dcc0af0f6ca283967e44b85ce 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4184,6 +4184,7 @@ static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
 
 static void check_buffer_tree_ref(struct extent_buffer *eb)
 {
+       int refs;
        /* the ref bit is tricky.  We have to make sure it is set
         * if we have the buffer dirty.   Otherwise the
         * code to free a buffer can end up dropping a dirty
@@ -4204,6 +4205,10 @@ static void check_buffer_tree_ref(struct extent_buffer *eb)
         * So bump the ref count first, then set the bit.  If someone
         * beat us to it, drop the ref we added.
         */
+       refs = atomic_read(&eb->refs);
+       if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
+               return;
+
        spin_lock(&eb->refs_lock);
        if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                atomic_inc(&eb->refs);
@@ -4405,9 +4410,20 @@ static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
 
 void free_extent_buffer(struct extent_buffer *eb)
 {
+       int refs;
+       int old;
        if (!eb)
                return;
 
+       while (1) {
+               refs = atomic_read(&eb->refs);
+               if (refs <= 3)
+                       break;
+               old = atomic_cmpxchg(&eb->refs, refs, refs - 1);
+               if (old == refs)
+                       return;
+       }
+
        spin_lock(&eb->refs_lock);
        if (atomic_read(&eb->refs) == 2 &&
            test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags))