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

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Message-ID: <1342595730.3669.70.camel@pasglop>
Date:	Wed, 18 Jul 2012 17:15:30 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jiang Liu <jiang.liu@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Tony Luck <tony.luck@...el.com>,
	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>,
	David Gibson <david@...son.dropbear.id.au>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] mm: setup pageblock_order before it's used by sparse

On Mon, 2012-07-02 at 20:25 -0700, Yinghai Lu wrote:
> > That means pageblock_order is always set to "MAX_ORDER - 1", not sure
> > whether this is intended. And it has the same issue as IA64 of wasting
> > memory if CONFIG_SPARSE is enabled.
> 
> adding BenH, need to know if it is powerpc intended.
> 
> >
> > So it would be better to keep function set_pageblock_order(), it will
> > fix the memory wasting on both IA64 and PowerPC.
> 
> Should setup pageblock_order as early as possible to avoid confusing.

Hrm, HPAGE_SHIFT is initially 0 because we only know at runtime what
huge page sizes are going to be supported (if any).

The business with pageblock_order is new to me and does look bogus today
indeed. But not a huge deal either. Our MAX_ORDER is typically 9 (64K
pages) or 13 (4K pages) and our standard huge page size is generally 16M
so there isn't a big difference here.

Still, maybe something worth looking into...

Cheers,
Ben.


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