ext4: Don't normalize an falloc request if it can fit in 1 extent.

If an fallocate request fits in EXT_UNINIT_MAX_LEN, then set the
EXT4_GET_BLOCKS_NO_NORMALIZE flag. For larger fallocate requests,
let mballoc.c normalize the request.

This fixes a problem where large requests were being split into
non-contiguous extents due to commit 556b27abf73: ext4: do not
normalize block requests from fallocate.

Testing: 
*) Checked that 8.x MB falloc'ed files are still laid down next to
each other (contiguously).
*) Checked that the maximum size extent (127.9MB) is allocated as 1
extent.
*) Checked that a 1GB file is somewhat contiguous (often 5-6
non-contiguous extents now).
*) Checked that a 120MB file can still be falloc'ed even if there are
no single extents large enough to hold it.

Signed-off-by: Greg Harm <gharm@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 8 insertions, 2 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index a5c8caaaa099..2798945a1920 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4337,10 +4337,16 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
                 trace_ext4_fallocate_exit(inode, offset, max_blocks, ret);
                 return ret;
         }
-        flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT |
-                EXT4_GET_BLOCKS_NO_NORMALIZE;
+        flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT;
         if (mode & FALLOC_FL_KEEP_SIZE)
                 flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
+        /*
+         * Don't normalize the request if it can fit in one extent so
+         * that it doesn't get unnecessarily split into multiple
+         * extents.
+         */
+        if (len <= EXT_UNINIT_MAX_LEN << blkbits)
+                flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
 retry:
         while (ret >= 0 && ret < max_blocks) {
                 map.m_lblk = map.m_lblk + ret;