Re: [PATCH] improve the performance of large sequential write NFS workloads

Peter Zijlstra
2010-01-06T19:07:56Z

On Wed, 2010-01-06 at 13:52 -0500, Trond Myklebust wrote:
> On Wed, 2010-01-06 at 19:37 +0100, Peter Zijlstra wrote:
> > On Wed, 2010-01-06 at 13:26 -0500, Trond Myklebust wrote:
> > > OK. It looks as if the only key to finding out how many unstable writes
> > > we have is to use global_page_state(NR_UNSTABLE_NFS), so we can't
> > > specifically target our own backing-dev.
> >
> > Would be a simple matter of splitting BDI_UNSTABLE out from
> > BDI_RECLAIMABLE, no?
> >
> > Something like
>
> OK. How about if we also add in a bdi->capabilities flag to tell that we
> might have BDI_UNSTABLE? That would allow us to avoid the potentially
> expensive extra calls to bdi_stat() and bdi_stat_sum() for the non-nfs
> case?

The bdi_stat_sum() in the error limit is basically the only such
expensive op, but I suspect we might hit that more than enough. So sure
that sounds like a plan.