btrfs compression: reuse recently used workspace

Add compression `workspace' in free_workspace() to
`idle_workspace' list head, instead of tail. So we have
better chances to reuse most recently used `workspace'.

Signed-off-by: Sergey Senozhatsky <[e-mail]>
Reviewed-by: David Sterba <[e-mail]>
Signed-off-by: Chris Mason <[e-mail]>

fs/btrfs/compression.c

···
 
 	spin_lock(workspace_lock);
 	if (*num_workspace < num_online_cpus()) {
-		list_add_tail(workspace, idle_workspace);
+		list_add(workspace, idle_workspace);
 		(*num_workspace)++;
 		spin_unlock(workspace_lock);
 		goto wake;