Re: [PATCH v4] staging: lustre: mdc: manage number of modify RPCs in flight

[James Simmons]

> On Thu, Nov 10, 2016 at 10:51:13AM -0500, James Simmons wrote:
> > From: Gregoire Pichon <gregoire.pichon@xxxxxxxx>
> > 
> > This patch is the main client part of a new feature that supports
> > multiple modify metadata RPCs in parallel. Its goal is to improve
> > metadata operations performance of a single client, while maintening
> > the consistency of MDT reply reconstruction and MDT recovery
> > mechanisms.
> > 
> > It allows to manage the number of modify RPCs in flight within
> > the client obd structure and to assign a virtual index (the tag) to
> > each modify RPC to help server side cleaning of reply data.
> > 
> > The mdc component uses this feature to send multiple modify RPCs
> > in parallel.
> 
> Is this a new feature?  Why should we take this now and not just wait
> until the code is out of staging?

Yes on the server side. So the problem on our meta data servers couldn't
handle writing mulitiple bits of data to the back end disk at ths same
time.

One client side the issue was the metadata operations were being 
serialized by a mutex in the MDC layer. That is what this patch fixed.
So for the client it would be a performance improvement patch.