1 files changed, 26 insertions, 4 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0554c48cb1fd..d53e20f53103 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -117,11 +117,33 @@ static ext4_fsblk_t ext4_ext_find_goal(struct inode *inode,
                 struct ext4_extent *ex;
                 depth = path->p_depth;
 
-                /* try to predict block placement */
+                /*
+                 * Try to predict block placement assuming that we are
+                 * filling in a file which will eventually be
+                 * non-sparse --- i.e., in the case of libbfd writing
+                 * an ELF object sections out-of-order but in a way
+                 * the eventually results in a contiguous object or
+                 * executable file, or some database extending a table
+                 * space file.  However, this is actually somewhat
+                 * non-ideal if we are writing a sparse file such as
+                 * qemu or KVM writing a raw image file that is going
+                 * to stay fairly sparse, since it will end up
+                 * fragmenting the file system's free space.  Maybe we
+                 * should have some hueristics or some way to allow
+                 * userspace to pass a hint to file system,
+                 * especiially if the latter case turns out to be
+                 * common.
+                 */
                 ex = path[depth].p_ext;
-                if (ex)
-                        return (ext4_ext_pblock(ex) +
-                                (block - le32_to_cpu(ex->ee_block)));
+                if (ex) {
+                        ext4_fsblk_t ext_pblk = ext4_ext_pblock(ex);
+                        ext4_lblk_t ext_block = le32_to_cpu(ex->ee_block);
+
+                        if (block > ext_block)
+                                return ext_pblk + (block - ext_block);
+                        else
+                                return ext_pblk - (ext_block - block);
+                }
 
                 /* it looks like index is empty;
                  * try to find starting block from index itself */