[PATCH 1/8] blkcg, writeback: Add wbc->no_wbc_acct

[Tejun Heo]

When writeback IOs are bounced through async layers, the IOs should
only be accounted against the wbc from the original bdi writeback to
avoid confusing cgroup inode ownership arbitration.  Add
wbc->no_wbc_acct to allow disabling wbc accounting.  This will be used
make btfs compression work well with cgroup IO control.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 fs/fs-writeback.c         | 2 +-
 include/linux/writeback.h | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 36855c1f8daf..6c8061a49ca0 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -721,7 +721,7 @@ void wbc_account_io(struct writeback_control *wbc, struct page *page,
 	 * behind a slow cgroup.  Ultimately, we want pageout() to kick off
 	 * regular writeback instead of writing things out itself.
 	 */
-	if (!wbc->wb)
+	if (!wbc->wb || wbc->no_wbc_acct)
 		return;
 
 	id = mem_cgroup_css_from_page(page)->id;
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 738a0c24874f..b8f5f000cde4 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -68,6 +68,7 @@ struct writeback_control {
 	unsigned for_reclaim:1;		/* Invoked from the page allocator */
 	unsigned range_cyclic:1;	/* range_start is cyclic */
 	unsigned for_sync:1;		/* sync(2) WB_SYNC_ALL writeback */
+	unsigned no_wbc_acct:1;		/* skip wbc IO accounting */
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct bdi_writeback *wb;	/* wb this writeback is issued under */
 	struct inode *inode;		/* inode being written out */
-- 
2.17.1