Re: Make sm-notify faster if there are no servers to notify

[Steve Dickson <SteveD@redhat.com>]

J. Bruce Fields wrote:
> On Wed, Oct 29, 2008 at 04:30:32PM -0400, Chuck Lever wrote:
>> I assume sync() is required because this logic performs a rename as well 
>> as a simple write?
> 
> I think an fsync() on the containing directory (together with an fsync()
> of the file itself) would do the job if you wanted to avoid the globaly
> sync().  I don't think ext3 is capable of doing anything finer-grained
> than a whole-filesystem sync, though, so this doesn't help many people
> in practice right now.
> 
> In any case, the rename adds an extra level of safety by ensuring the
> nsm state is updated atomically, so we shouldn't get rid of it.
> 
>>> Anyway, I think the nsm state updating shouldn't matter if you don't
>>> even have any peers to notify.
>> It probably does matter.
>>
>> When a system is initially installed, it likely does not have a state  
>> file in /var/lib/nfs.  This may be harmless if it's not present;  
>> rpc.statd probably does the right thing in this case.
> 
> The "right thing" in that case would be, I guess, to create a state file
> with "0" in it.  It doesn't do that.  So this patch *does* break stuff.
> Oops!
> 
> So should we revert it and do something else, or patch statd to create
> a new state file if necessary?
I have to agree with Chuck, that managing the state file from one 
place is desirable... Although does it make sense to move that management
into a init script? Maybe insuring the state is different before any
daemons are started? Would we still need the sync()? 
  
> 
>> However, the rest of the logic in nsm_get_state() is needed to bump the 
>> system's state value properly after every reboot.  It may be  
>> inconsequential if there were no mounts or no NFS clients during the  
>> last reboot, but this is subtle.  I wouldn't bet on it.
> 
> If the state is only every communicated to hosts by notifications, then
> if we're not notifying, the update of the state can't matter.
I had the same notion... If there are no clients to notify, why would 
any clients care if our state changed??  With that said.... I do have a
sinking feeling that this patch will come back to bite us... 
It was just too easy of a fix... :-)

steved.