linux-kernel - Re: [PATCH 02/10] vmscan: move priority variable into scan

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Message-Id: <20100528113404.7E18.A69D9226@jp.fujitsu.com>
Date:	Fri, 28 May 2010 11:39:54 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Chris Mason <chris.mason@...cle.com>,
	Dave Chinner <david@...morbit.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 02/10] vmscan: move priority variable into scan_control

Hi

> Sorry for the long delay on this. I got distracted by the anon_vma and
> page migration stuff.

Sorry for the delay too. I don't have enough development time recently ;)
I had tested this patch series a while. but now they need to rebase and retest. that's sad.

> On Sat, Apr 17, 2010 at 12:48:20AM +0200, Johannes Weiner wrote:
> > On Thu, Apr 15, 2010 at 06:21:35PM +0100, Mel Gorman wrote:
> > > From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > > 
> > > Now very lots function in vmscan have `priority' argument. It consume
> > > stack slightly. To move it on struct scan_control reduce stack.
> > 
> > I don't like this much because it obfuscates value communication.
> > 
> > Functions no longer have obvious arguments and return values, as it's all
> > passed hidden in that struct.
> > 
> > Do you think it's worth it?  I would much rather see that thing die than
> > expand on it...
> 
> I don't feel strongly enough to fight about it and reducing stack usage here
> isn't the "fix" anyway. I'll drop this patch for now.

I'm ok either.


> That aside, the page reclaim algorithm maintains a lot of state and the
> "priority" is part of that state. While the struct means that functions might
> not have obvious arguments, passing the state around as arguments gets very
> unwieldly very quickly. I don't think killing scan_control would be as
> nice as you imagine although I do think it should be as small as
> possible.

I don't have strong opinion. I think both you and Hannes were talking correct thing.
But Hannes seems to have more strong opinion. then, I'm tend to drop this one.

Thanks.


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