[Lustre-devel] Queries regarding LDLM_ENQUEUE

[bzzz.tomas at gmail.com <bzzz.tomas@gmail.com>]

On 10/20/10 5:30 PM, Eric Barton wrote:
> I do like the idea of a collective open, but I'm wondering if it can be
> implemented simply enough to be worth the effort.  True, it avoids the O(n)
> load on the server of all the clients (re)populating their namespace
> caches, but it's only useful for parallel jobs - a scale-out NAS style
> workload can't benefit.  Ultimately the O(n) will have to be replaced with
> something that scales O(log n) (e.g. with a fat tree of caching proxy
> servers).

in long-term I'd prefer proxy approach because this way we could improve
number of cases, including existing POSIX apps doing open, stat, etc.

>>>> another idea was to do whole path traversal on MDS within a single
>>>> RPC.  bug that'd require amount of changes to llite and/or VFS and
>>>> keep MDS a bottleneck.
>
> That's an optimization rather than a scalability feature.  How much does
> it complicate the code?  I'd hate to see something new tricky and fragile
> complicate further development.

yes, this is an optimization. good thing here is that single client can
benefit a lot from this (replacing few RPCs with a single one). bad
thing is that it can be quite quite complicated on the client side (the
server side's part looks OK).

thanks, z