Messages in this thread | | | Date | Tue, 21 Dec 2021 09:56:23 +0100 | From | Christoph Hellwig <> | Subject | Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone |
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On Fri, Dec 17, 2021 at 11:38:27AM +0000, Hyeonggon Yoo wrote: > My understanding is any buffer requested from kmalloc (without > GFP_DMA/DMA32) can be used by device driver because it allocates > continuous physical memory. It doesn't mean that buffer allocated > with kmalloc is free of addressing limitation.
Yes.
> > the addressing limitation comes from the capability of device, not > allocation size. if you allocate memory using alloc_pages() or kmalloc(), > the device has same limitation. and vmalloc can't be used for > devices because they have no MMU.
vmalloc can be used as well, it just needs to be setup as a scatterlist and needs a little lover for DMA challenged platforms with the invalidate_kernel_vmap_range and flush_kernel_vmap_range helpers.
> But we can map memory outside DMA zone into bounce buffer (which resides > in DMA zone) using DMA API.
Yes, although in a few specific cases the bounce buffer could also come from somewhere else.
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