-----Original Message-----
From: Linuxppc-dev [mailto:linuxppc-dev-bounces+tie-
fei.zang=3Dfreescale.com@lists.ozlabs.org] On Behalf Of Benjamin
Herrenschmidt
Sent: Tuesday, July 24, 2012 11:09 AM
To: Tabi Timur-B04825
Cc: Wood Scott-B07421; Hu Mingkai-B21284; linuxppc-dev@lists.ozlabs.org;
Xie Shaohui-B21989; Chen Yuanquan-B41889
Subject: Re: [PATCH] powerpc/mm: add ZONE_NORMAL zone for 64 bit kernel
=20
On Mon, 2012-07-23 at 18:36 -0500, Timur Tabi wrote:

quoted

The DMA zone only kicks in if the DMA mask is set to a size smaller
that
available physical memory.  Sane HW should set the DMA mask to
DMA_BIT_MASK(36).  And we have plenty of sane HW on our SOCs, but not
every device is like that.

The whole point behind this patch is that some drivers are setting a
DMA
mask of 32, but still getting memory above 4GB.

=20
Sure but I don't want to create the zones in the first place (and thus
introduce the added pressure on the memory management) on machines that
don't need it.

OK, then how do you think Scott's suggestion to add a configurable threshol=
d?
Roy