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Message-ID: <5604220F.503@fb.com> Date: Thu, 24 Sep 2015 10:17:19 -0600 From: Jens Axboe <axboe@...com> To: Tejun Heo <tj@...nel.org>, Artem Bityutskiy <dedekind1@...il.com> CC: "Theodore Ts'o" <tytso@....edu>, <axboe@...nel.dk>, <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>, <lizefan@...wei.com>, <cgroups@...r.kernel.org>, <hannes@...xchg.org>, <kernel-team@...com>, <adilger.kernel@...ger.ca>, <linux-ext4@...r.kernel.org>, Dexuan Cui <decui@...rosoft.com> Subject: Re: [PATCH cgroup/for-4.3-fixes] cgroup, writeback: don't enable cgroup writeback on traditional hierarchies On 09/23/2015 03:07 PM, Tejun Heo wrote: > 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@...nel.org> > Reported-by: Artem Bityutskiy <dedekind1@...il.com> > Reported-by: Dexuan Cui <decui@...rosoft.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 > --- > 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(-) I'll ack this since it works around both the corruption issue and the performance regression, so we can avoid having to revert parts of this. And I know you'll keep hunting and get the real issue fixed in the mean time. Acked-by: Jens Axboe <axboe@...com> -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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