[PATCH] powerpc/mm: add ZONE_NORMAL zone for 64 bit kernel

Zang Roy-R61911 r61911 at freescale.com
Tue Jul 24 13:59:40 EST 2012



> -----Original Message-----
> From: Linuxppc-dev [mailto:linuxppc-dev-bounces+tie-
> fei.zang=freescale.com at 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 at lists.ozlabs.org;
> Xie Shaohui-B21989; Chen Yuanquan-B41889
> Subject: Re: [PATCH] powerpc/mm: add ZONE_NORMAL zone for 64 bit kernel
> 
> On Mon, 2012-07-23 at 18:36 -0500, Timur Tabi wrote:
> > 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.
> 
> 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 threshold?
Roy



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