Btrfs: add a check to decide if we should defrag the range

If our file's layout is as follows:
| hole | data1 | hole | data2 |

we do not need to defrag this file, because this file has holes and
cannot be merged into one extent.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 35 insertions, 1 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index de46fa218590..6c39d1a55907 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -784,6 +784,31 @@ none:
         return -ENOENT;
 }
 
+/*
+ * Validaty check of prev em and next em:
+ * 1) no prev/next em
+ * 2) prev/next em is an hole/inline extent
+ */
+static int check_adjacent_extents(struct inode *inode, struct extent_map *em)
+{
+        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
+        struct extent_map *prev = NULL, *next = NULL;
+        int ret = 0;
+
+        read_lock(&em_tree->lock);
+        prev = lookup_extent_mapping(em_tree, em->start - 1, (u64)-1);
+        next = lookup_extent_mapping(em_tree, em->start + em->len, (u64)-1);
+        read_unlock(&em_tree->lock);
+
+        if ((!prev || prev->block_start >= EXTENT_MAP_LAST_BYTE) &&
+            (!next || next->block_start >= EXTENT_MAP_LAST_BYTE))
+                ret = 1;
+        free_extent_map(prev);
+        free_extent_map(next);
+
+        return ret;
+}
+
 static int should_defrag_range(struct inode *inode, u64 start, u64 len,
                                int thresh, u64 *last_len, u64 *skip,
                                u64 *defrag_end)
@@ -821,8 +846,16 @@ static int should_defrag_range(struct inode *inode, u64 start, u64 len,
         }
 
         /* this will cover holes, and inline extents */
-        if (em->block_start >= EXTENT_MAP_LAST_BYTE)
+        if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
+                ret = 0;
+                goto out;
+        }
+
+        /* If we have nothing to merge with us, just skip. */
+        if (check_adjacent_extents(inode, em)) {
                 ret = 0;
+                goto out;
+        }
 
         /*
          * we hit a real extent, if it is big don't bother defragging it again
@@ -830,6 +863,7 @@ static int should_defrag_range(struct inode *inode, u64 start, u64 len,
         if ((*last_len == 0 || *last_len >= thresh) && em->len >= thresh)
                 ret = 0;
 
+out:
         /*
          * last_len ends up being a counter of how many bytes we've defragged.
          * every time we choose not to defrag an extent, we reset *last_len