> On Jun 28, 2016, at 22:00, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> On Tue, 2016-06-28 at 21:03 +0800, Yan, Zheng wrote:
>> On Tue, Jun 28, 2016 at 3:07 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>>>
>>> I'm eyeballing how to make ceph dentry revalidation occur in rcu-walk
>>> mode in the kernel cephfs client. It looks fairly straightforward, but
>>> for one thing:
>>>
>>> dentry_lease_is_valid queues an asynchronous lease renewal if we're
>>> halfway to the next lease renewal time:
>>>
>>> if (session) {
>>> ceph_mdsc_lease_send_msg(session, dir, dentry,
>>> CEPH_MDS_LEASE_RENEW, seq);
>>> ceph_put_mds_session(session);
>>> }
>>>
>>> That can sleep, so we have to drop out of rcu walk mode in that case.
>>>
>>> Is this lease renewal strictly necessary? I can make the code drop out
>>> of rcuwalk mode and try again in that case, but if this is just an
>>> opportunistic thing, then it may be better for performance to take a
>>> pass on renewing the lease early if we're still in RCU walk mode.
>>>
>> dentry_lease_is_valid is the only place that renew lease. I think it's
>> better to drop out of rcuwalk and try again
>>
>> Regards
>> Yan, Zheng
>>
>
> That seems really odd to me.
>
> That call is only ever done in the d_revalidate codepath, so you'll
> only get a lease renewal when you have repeated path-based access to an
> existing dentry.
>
> Maybe this means that I don't really understand ceph leases. More
> questions...
>
> What exactly does the lease cover here?
Lease covers dentry. MDS revoke release before changing dentry’s linkage. If client access a dentry frequently, it should renew the dentry lease when necessary. If dentry lease expires, client need to send a lookup request if it want to access the dentry.
Yan, Zheng
>
> Shouldn't we be renewing it even if we're _not_ doing any path-based
> access? For instance, if I open a file and issue reads and writes
> against it, that doesn't involve pathnames and the lease doesn't get an
> explicit renewal. Doesn't it still need to be renewed though?
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
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