linux-kernel - Re: [PATCH 8/8] vm: Add an tuning knob for vm.max_writeback

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Date:	Wed, 9 Sep 2009 14:37:46 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Artem Bityutskiy <dedekind1@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"david@...morbit.com" <david@...morbit.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"jack@...e.cz" <jack@...e.cz>, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH 8/8] vm: Add an tuning knob for vm.max_writeback_mb

On Wed, Sep 09 2009, Wu Fengguang wrote:
> On Wed, Sep 09, 2009 at 08:28:06PM +0800, Christoph Hellwig wrote:
> > On Wed, Sep 09, 2009 at 05:29:01PM +0800, Wu Fengguang wrote:
> > > It seems that balance_dirty_pages() is not coupled with MAX_WRITEBACK_PAGES. 
> > > Instead it uses the much smaller (ratelimit_pages + ratelimit_pages / 2).
> > 
> > With Jen's writeback patches applied balance_dirty_pages does not start
> > writeback itself anymore but calls bdi_start_writeback to let the
> > flusher thread do it.
> > 
> > it would be good if we do any writeback tuning ontop of these patches..
> 
> Ah OK. I'm using latest linux-next and expected his patches to be there..

They are there, have been for months! But I think Christoph is a little
confused, we'll still do writeback inline from balance_dirty_pages(). It
does writeback_inodes_wbc(), which does not schedule async writeout.

So if your patches are based and tested off -next, you should be good.

-- 
Jens Axboe

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