Ocfs2/move_extents: helper to calculate the defraging length in one run.

The helper is to calculate the defrag length in one run according to a threshold,
it will proceed doing defragmentation until the threshold was meet, and skip a
LARGE extent if any.

Signed-off-by: Tristan Ye <tristan.ye@oracle.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c
index ae15c998a82a..1c822e08fea0 100644
--- a/fs/ocfs2/move_extents.c
+++ b/fs/ocfs2/move_extents.c
@@ -797,3 +797,33 @@ out:
 
         return ret;
 }
+
+/*
+ * Helper to calculate the defraging length in one run according to threshold.
+ */
+static void ocfs2_calc_extent_defrag_len(u32 *alloc_size, u32 *len_defraged,
+                                         u32 threshold, int *skip)
+{
+        if ((*alloc_size + *len_defraged) < threshold) {
+                /*
+                 * proceed defragmentation until we meet the thresh
+                 */
+                *len_defraged += *alloc_size;
+        } else if (*len_defraged == 0) {
+                /*
+                 * XXX: skip a large extent.
+                 */
+                *skip = 1;
+        } else {
+                /*
+                 * split this extent to coalesce with former pieces as
+                 * to reach the threshold.
+                 *
+                 * we're done here with one cycle of defragmentation
+                 * in a size of 'thresh', resetting 'len_defraged'
+                 * forces a new defragmentation.
+                 */
+                *alloc_size = threshold - *len_defraged;
+                *len_defraged = 0;
+        }
+}