> -----Original Message----- > From: Linuxppc-dev [mailto:linuxppc-dev-bounces+tie- > fei.zang=freescale....@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 > > 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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