Commit 2a0f7f57 authored by Li Zefan's avatar Li Zefan Committed by Chris Mason
Browse files

Btrfs: fix recursive auto-defrag

Follow those steps:

  # mount -o autodefrag /dev/sda7 /mnt
  # dd if=/dev/urandom of=/mnt/tmp bs=200K count=1
  # sync
  # dd if=/dev/urandom of=/mnt/tmp bs=8K count=1 conv=notrunc

and then it'll go into a loop: writeback -> defrag -> writeback ...

It's because writeback writes [8K, 200K] and then writes [0, 8K].

I tried to make writeback know if the pages are dirtied by defrag,
but the patch was a bit intrusive. Here I simply set writeback_index
when we defrag a file.
Signed-off-by: default avatarLi Zefan <>
Signed-off-by: default avatarChris Mason <>
parent b6316429
......@@ -1055,6 +1055,13 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
if (!max_to_defrag)
max_to_defrag = last_index - 1;
* make writeback starts from i, so the defrag range can be
* written sequentially.
if (i < inode->i_mapping->writeback_index)
inode->i_mapping->writeback_index = i;
while (i <= last_index && defrag_count < max_to_defrag) {
* make sure we stop running if someone unmounts
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