Messages in this thread | | | Subject | Re: [PATCH 5/8] arm64: use ZONE_DMA on DMA addressing limited devices | From | Robin Murphy <> | Date | Thu, 1 Aug 2019 17:07:54 +0100 |
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On 2019-08-01 4:44 pm, Nicolas Saenz Julienne wrote: > On Wed, 2019-07-31 at 18:07 +0100, Catalin Marinas wrote: >> On Wed, Jul 31, 2019 at 05:47:48PM +0200, Nicolas Saenz Julienne wrote: >>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c >>> index 1c4ffabbe1cb..f5279ef85756 100644 >>> --- a/arch/arm64/mm/init.c >>> +++ b/arch/arm64/mm/init.c >>> @@ -50,6 +50,13 @@ >>> s64 memstart_addr __ro_after_init = -1; >>> EXPORT_SYMBOL(memstart_addr); >>> >>> +/* >>> + * We might create both a ZONE_DMA and ZONE_DMA32. ZONE_DMA is needed if >>> there >>> + * are periferals unable to address the first naturally aligned 4GB of ram. >>> + * ZONE_DMA32 will be expanded to cover the rest of that memory. If such >>> + * limitations doesn't exist only ZONE_DMA32 is created. >>> + */ >> >> Shouldn't we instead only create ZONE_DMA to cover the whole 32-bit >> range and leave ZONE_DMA32 empty? Can__GFP_DMA allocations fall back >> onto ZONE_DMA32? > > Hi Catalin, thanks for the review. > > You're right, the GFP_DMA page allocation will fail with a nasty dmesg error if > ZONE_DMA is configured but empty. Unsurprisingly the opposite situation is fine > (GFP_DMA32 with an empty ZONE_DMA32).
Was that tested on something other than RPi4 with more than 4GB of RAM? (i.e. with a non-empty ZONE_NORMAL either way)
Robin.
> I switched to the scheme you're suggesting for the next version of the series. > The comment will be something the likes of this: > > /* > * We create both a ZONE_DMA and ZONE_DMA32. ZONE_DMA's size is decided based > * on whether the SoC's peripherals are able to address the first naturally > * aligned 4 GB of ram. > * > * If limited, ZONE_DMA covers that area and ZONE_DMA32 the rest of that 32 bit > * addressable memory. > * > * If not ZONE_DMA is expanded to cover the whole 32 bit addressable memory and > * ZONE_DMA32 is left empty. > */ > > Regards, > Nicolas > >
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