Messages in this thread | | | Date | Mon, 13 Dec 2021 08:49:19 +0100 | From | Christoph Hellwig <> | Subject | Re: [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when no managed pages |
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On Mon, Dec 13, 2021 at 03:39:25PM +0800, Baoquan He wrote: > > > As said at above, ia64 and riscv don't have ZONE_DMA at all, they just > > > cover low 4G with ZONE_DMA32 alone. > > > > If you do not have devices that are crap and cannot address the full > > memory then you dont need these special zones. > > I am not a DMA expert, with my understanding, on x86_64 and arm64, we > have PCIe devices which dma mask is 32bit
Yes, way to many, and they keep getting newly introduce as well. Also weirdo masks like 40, 44 or 48 bits.
> , means they can only address > ZONE_DMA32.
Yes and no. Offset between cpu physical and device address make this complicated, even ignoring iommus.
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