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: Tejun Heo <tj@xxxxxxxxxx> Reported-by: Artem Bityutskiy <dedekind1@xxxxxxxxx> Reported-by: Dexuan Cui <decui@xxxxxxxxxxxxx> Link: http://lkml.kernel.org/g/1443012552.19983.209.camel@xxxxxxxxx Link: http://lkml.kernel.org/g/f30d4a6aa8a546ff88f73021d026a453@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx --- Hello, So, this should make the regression go away. It doesn't fix the underlying bugs but they shouldn't get triggered by people not experimenting with cgroup. I'm gonna keep digging the underlying issues but this should make the regressions go away. If it's okay, I think it'd be better to route this through cgroup/for-4.3-fixes as it's gonna cause a conflict with for-4.4 branch and handling the merge there is easier. Thanks. include/linux/backing-dev.h | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index 5a5d79e..d5eb4ad1 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -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); } -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
