On 05/24/2018 04:23 PM, Ilya Dryomov wrote:
On Thu, May 24, 2018 at 5:27 AM, Dongsheng Yang
<dongsheng.yang@xxxxxxxxxxxx> wrote:
Default value of osd_request_timeout is 0 means never timeout,
and we can set this value in rbd mapping with -o "osd_request_timeout=XX".
But we can't change this value online.
Hi Dongsheng,
Changing just osd_request_timeout won't do anything about outstanding
requests waiting for the acquisition of the exclusive lock. This is an
rbd problem and should be dealt with in rbd.c.
Yes, we are using images without exclusive-lock.
And yes, the -ETIMEDOUT will try to aquire lock again and again currently,
we need to handle it properly.
[Question 1]: Why we need to set osd_request_timeout?
When we are going to reboot a node which have krbd devices mapped,
even with the rbdmap.service enabled, we will be blocked
in shuting down if the ceph cluster is not working.
Especially, If we have three controller nodes which is running as ceph mon,
but at the same time, there are some k8s pod with krbd devices on this nodes,
then we can't shut down the last controller node when we want to shutdown
all nodes, because when we are going to shutdown last controller node, the
ceph cluster is not reachable.
Why can't rbd images be unmapped in a proper way before the cluster is
shutdown?
That's optional, that's another solution in our plan. But this solution
can't solve the problem if the ceph cluster is not working and we
can't recover it soon, then we can't reboot nodes and the all IO
threads is in D state.
[Question 2]: Why don't we use rbd map -o "osd_request_timeout=XX"?
We don't want to set the osd_request_timeout in rbd device whole lifecycle,
there would be some problem in networking or cluster recovery to make
the request timeout. This would make the fs readonly and application down.
[Question 3]: How can this patch solve this problems?
With this patch, we can map rbd device with default value of osd_reques_timeout,
means never timeout, then we can solve the problem mentioned Question 2.
At the same time we can set the osd_request_timeout to what we need,
in system shuting down, for example, we can do this in rbdmap.service.
then we can make sure we can shutdown or reboot host normally no matter
ceph cluster is working well or not. This can solve the problem mentioned
in Question 1.
The plan is to add a new unmap option, so one can do "rbd unmap -o
full-force", as noted in https://tracker.ceph.com/issues/20927. This
is an old problem but it's been blocked on various issues in libceph.
Most of them look like they will be resolved in 4.18, bringing better
support for "umount -f" in kcephfs. We should be able to reuse that
work for "rbd unmap -o full-force".
But even we have a full-force unmap for rbd device, we need to umount
the fs first, e.g ext4. When we do umount fs before rbd unmap, we will
be blocked, and the umount process would be in D state.
Thanx
Thanks,
Ilya
--
To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
