linux-kernel - Re: [PATCH] mm: setup pageblock_order before it's used by sparse

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Message-ID: <20120704092006.GH14154@suse.de>
Date:	Wed, 4 Jul 2012 10:20:06 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Jiang Liu <jiang.liu@...wei.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Xishi Qiu <qiuxishi@...wei.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Keping Chen <chenkeping@...wei.com>, linux-mm@...ck.org,
	stable@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jiang Liu <liuj97@...il.com>
Subject: Re: [PATCH] mm: setup pageblock_order before it's used by sparse

On Wed, Jul 04, 2012 at 09:40:30AM +0800, Jiang Liu wrote:
> > It's a bit ugly calling set_pageblock_order() from both sparse_init()
> > and from free_area_init_core().  Can we find a single place from which
> > to call it?  It looks like here:
> > 
> > --- a/init/main.c~a
> > +++ a/init/main.c
> > @@ -514,6 +514,7 @@ asmlinkage void __init start_kernel(void
> >  		   __stop___param - __start___param,
> >  		   -1, -1, &unknown_bootoption);
> >  
> > +	set_pageblock_order();
> >  	jump_label_init();
> >  
> >  	/*
> > 
> > would do the trick?
> > 
> > (free_area_init_core is __paging_init and set_pageblock_order() is
> > __init.  I'm too lazy to work out if that's wrong)
> 
> Hi Andrew,
> 	Thanks for you comments. Yes, this's an issue. 
> And we are trying to find a way to setup  pageorder_block as 
> early as possible. Yinghai has suggested a good way for IA64,
> but we still need help from PPC experts because PPC has the 
> same issue and I'm not familiar with PPC architecture. 
> We will submit another patch once we find an acceptable
> solution here.

I think it's overkill to try and do this on a per-architecture basis unless
you are aware of a case where the per-architecture code cares about the
value of pageblock_order. I find it implausible that the architecture
needs to know the value very early in boot as pageblock_order is part of
the arch-independent memory model. Andrew's suggestion seems reasonable
to me once the section mess is figured out.

-- 
Mel Gorman
SUSE Labs
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