Messages in this thread | | | Date | Fri, 27 Jan 2023 07:35:55 +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 10:51:17AM -0800, Dave Hansen wrote: > > Also, what are the practical implications here? There are obviously an > ever decreasing number of 32-bit DMA devices out there. Somebody that > has one and uses this option might be sad because now they're stuck > using ZONE_DMA which is quite tiny. > > What other ZONE_DMA32 users are left? Will anyone else care? There is > some DMA32 slab and vmalloc() functionality remaining. Is it impacted?
DMA32 never supported lab. But < 64-bit DMA device are unfortunately still not uncommon, and configuring out ZONE_DMA32 breaks them pretty badly as we guarantee that a DMA mask of 32-bit always works.
So I'm not only very much against this patch, but also the currently existing way to configure out ZONE_DMA32 on arm64, which needs to go away.
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.
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