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Subject: Re: [PATCH] mm: setup pageblock_order before it's used by sparse
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Yinghai Lu <yinghai@kernel.org>
Cc: Jiang Liu <jiang.liu@huawei.com>,
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Date: Wed, 18 Jul 2012 17:15:30 +1000
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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.