Messages in this thread | | | Date | Fri, 27 Jan 2023 08:07:05 +0100 | From | Christoph Hellwig <> | Subject | Re: [RFC] mm: Allow ZONE_DMA32 to be disabled via kernel command line |
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On Thu, Jan 26, 2023 at 10:52:43PM -0800, H. Peter Anvin wrote: > >If people want ZONE_DMA32 to go away we need something to replace > >it first, like a large enough CMA region in the 32-bit addressable > >range. > > Not to mention all kinds of odd masks like 30, 31, 39, 40, 46, ... bits.
Yes. Out of those all >= 32 are falling straight into ZONE_DM32, the lower ones we do a first try in ZONE_DMA32 and then fall back to ZONE_DMA. <= 29 mask OTOH are really rate in modern systems for actual devices. So with a CMA region for what is currently ZONE_DMA and one for the first 1G we'd probably cover most of what's actually needed for x86_64. Of course on 32-bit architetures things become a lot more complicated due to highmem.
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