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

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Date:	Wed, 23 Dec 2009 20:12:54 +0100
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Steve Rago <sar@...-labs.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"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
Subject: Re: [PATCH] improve the performance of large sequential write NFS
 workloads

On Wed, 2009-12-23 at 19:05 +0100, Jan Kara wrote: 
> On Wed 23-12-09 15:21:47, Trond Myklebust wrote:
> > @@ -474,6 +482,18 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
> >  	}
> >  
> >  	spin_lock(&inode_lock);
> > +	/*
> > +	 * Special state for cleaning NFS unstable pages
> > +	 */
> > +	if (inode->i_state & I_UNSTABLE_PAGES) {
> > +		int err;
> > +		inode->i_state &= ~I_UNSTABLE_PAGES;
> > +		spin_unlock(&inode_lock);
> > +		err = commit_unstable_pages(inode, wait);
> > +		if (ret == 0)
> > +			ret = err;
> > +		spin_lock(&inode_lock);
> > +	}
>   I don't quite understand this chunk: We've called writeback_single_inode
> because it had some dirty pages. Thus it has I_DIRTY_DATASYNC set and a few
> lines above your chunk, we've called nfs_write_inode which sent commit to
> the server. Now here you sometimes send the commit again? What's the
> purpose?

We no longer set I_DIRTY_DATASYNC. We only set I_DIRTY_PAGES (and later
I_UNSTABLE_PAGES).

The point is that we now do the commit only _after_ we've sent all the
dirty pages, and waited for writeback to complete, whereas previously we
did it in the wrong order.

Cheers
  Trond
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