Btrfs: use percpu counter for fs_info->delalloc_bytes

fs_info->delalloc_bytes is accessed very frequently, so use percpu
counter instead of the u64 variant for it to reduce the lock
contention.

This patch also fixed the problem that we access the variant
without the lock protection.At worst, we would not flush the
delalloc inodes, and just return ENOSPC error when we still have
some free space in the fs.

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

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 174c4d5c692c..115d1646bf50 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3760,7 +3760,8 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
         space_info = block_rsv->space_info;
 
         smp_mb();
-        delalloc_bytes = root->fs_info->delalloc_bytes;
+        delalloc_bytes = percpu_counter_sum_positive(
+                                                &root->fs_info->delalloc_bytes);
         if (delalloc_bytes == 0) {
                 if (trans)
                         return;
@@ -3799,7 +3800,8 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
                                 break;
                 }
                 smp_mb();
-                delalloc_bytes = root->fs_info->delalloc_bytes;
+                delalloc_bytes = percpu_counter_sum_positive(
+                                                &root->fs_info->delalloc_bytes);
         }
 }