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: Li Zefan <lizf@cn.fujitsu.com>
---
fs/btrfs/ioctl.c | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 970977a..7a10f94 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1047,6 +1047,13 @@ 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
-- 1.7.3.1
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On Thu, Oct 06, 2011 at 11:39:54AM +0800, Li Zefan wrote:> 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: Li Zefan <lizf@cn.fujitsu.com>Tested-by: David Sterba <dsterba@suse.cz>> --- > fs/btrfs/ioctl.c | 7 +++++++ > 1 files changed, 7 insertions(+), 0 deletions(-) > > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c > index 970977a..7a10f94 100644 > --- a/fs/btrfs/ioctl.c > +++ b/fs/btrfs/ioctl.c > @@ -1047,6 +1047,13 @@ 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 > -- 1.7.3.1 > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html-- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Oct 06, 2011 at 11:39:54AM +0800, Li Zefan wrote:> 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.Really nice and small fix. I''ll definitely send this for 3.1 -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html