btrfs: don't use async helpers for crcs when under IO limits
We want to avoid priority inversions from btrfs' async helpers when
using cgroups to control IO. The least complicated way is to avoid
the async helpers completely when we're not in the root cgroup for IO.
On modern hardware with crc32c acceleration, this has a very small
impact, but we want to do more benchmarks to make sure.
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e1a7f3c..f0529dd 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1967,6 +1967,15 @@ static blk_status_t btrfs_submit_bio_hook(void *private_data, struct bio *bio,
skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
+#ifdef CONFIG_BLK_CGROUP
+ /*
+ * if we're under IO controls, force a synchronous crc and
+ * IO submission so things get accounted in the proper slots.
+ */
+ if (!task_css_is_root(current, io_cgrp_id))
+ async = 0;
+#endif
+
if (btrfs_is_free_space_inode(BTRFS_I(inode)))
metadata = BTRFS_WQ_ENDIO_FREE_SPACE;
@@ -1986,10 +1995,10 @@ static blk_status_t btrfs_submit_bio_hook(void *private_data, struct bio *bio,
goto out;
}
goto mapit;
- } else if (async && !skip_sum) {
+ } else if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID) {
/* csum items have already been cloned */
- if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID)
- goto mapit;
+ goto mapit;
+ } else if (async && !skip_sum) {
/* we're doing a write, do the async checksumming */
ret = btrfs_wq_submit_bio(fs_info, bio, mirror_num, bio_flags,
bio_offset, inode,
