Commit 9badce00 authored by Tejun Heo's avatar Tejun Heo

cgroup, writeback: don't enable cgroup writeback on traditional hierarchies

inode_cgwb_enabled() gates cgroup writeback support.  If it returns
true, each inode is attached to the corresponding memory domain which
gets mapped to io domain.  It currently only tests whether the
filesystem and bdi support cgroup writeback; however, cgroup writeback
support doesn't work on traditional hierarchies and thus it should
also test whether memcg and iocg are on the default hierarchy.

This caused traditional hierarchy setups to hit the cgroup writeback
path inadvertently and ended up creating separate writeback domains
for each memcg and mapping them all to the root iocg uncovering a
couple issues in the cgroup writeback path.

cgroup writeback was never meant to be enabled on traditional
hierarchies.  Make inode_cgwb_enabled() test whether both memcg and
iocg are on the default hierarchy.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatarArtem Bityutskiy <dedekind1@gmail.com>
Reported-by: default avatarDexuan Cui <decui@microsoft.com>
Link: http://lkml.kernel.org/g/1443012552.19983.209.camel@gmail.com
Link: http://lkml.kernel.org/g/f30d4a6aa8a546ff88f73021d026a453@SIXPR30MB031.064d.mgd.msft.net
parent 0c986253
......@@ -13,6 +13,7 @@
#include <linux/sched.h>
#include <linux/blkdev.h>
#include <linux/writeback.h>
#include <linux/memcontrol.h>
#include <linux/blk-cgroup.h>
#include <linux/backing-dev-defs.h>
#include <linux/slab.h>
......@@ -252,13 +253,19 @@ int inode_congested(struct inode *inode, int cong_bits);
* @inode: inode of interest
*
* cgroup writeback requires support from both the bdi and filesystem.
* Test whether @inode has both.
* Also, both memcg and iocg have to be on the default hierarchy. Test
* whether all conditions are met.
*
* Note that the test result may change dynamically on the same inode
* depending on how memcg and iocg are configured.
*/
static inline bool inode_cgwb_enabled(struct inode *inode)
{
struct backing_dev_info *bdi = inode_to_bdi(inode);
return bdi_cap_account_dirty(bdi) &&
return cgroup_on_dfl(mem_cgroup_root_css->cgroup) &&
cgroup_on_dfl(blkcg_root_css->cgroup) &&
bdi_cap_account_dirty(bdi) &&
(bdi->capabilities & BDI_CAP_CGROUP_WRITEBACK) &&
(inode->i_sb->s_iflags & SB_I_CGROUPWB);
}
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment