tree b4e4fce2de1c4a9cc20227c8311672682027c802
parent 43703472e76dfa72d21c3ccb9fb577178393532b
author Miao Xie <miaox@cn.fujitsu.com> 1394085304 +0800
committer Josef Bacik <jbacik@fb.com> 1394215585 -0500

Btrfs: reclaim the reserved metadata space at background

Before applying this patch, the task had to reclaim the metadata space
by itself if the metadata space was not enough. And When the task started
the space reclamation, all the other tasks which wanted to reserve the
metadata space were blocked. At some cases, they would be blocked for
a long time, it made the performance fluctuate wildly.

So we introduce the background metadata space reclamation, when the space
is about to be exhausted, we insert a reclaim work into the workqueue, the
worker of the workqueue helps us to reclaim the reserved space at the
background. By this way, the tasks needn't reclaim the space by themselves at
most cases, and even if the tasks have to reclaim the space or are blocked
for the space reclamation, they will get enough space more quickly.

We needn't worry about the early enospc problem because all the reclaim work
is serialized by the lock.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>