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

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Message-ID: <1262804876.4049.66.camel@laptop>
Date:	Wed, 06 Jan 2010 20:07:56 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Steve Rago <sar@...-labs.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jens.axboe" <jens.axboe@...cle.com>,
	Peter Staubach <staubach@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] improve the performance of large sequential write NFS
 workloads

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.

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