Re: [Xen-devel] x86 swiotlb questions

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>> - The DMA bit widths can be set to different values in Xen and kernel, which
>> can
>> lead to surprising results, I would think. Shouldn't the kernel rather obtain
>> Xen's
>> value, so they are consistent?
>
>We would like to generalise Xen's heap allocator so that it keeps separate
>heaps for different bit widths. Then there would be no 'DMA width' or 'DMA
>pool' in Xen.

I already have patches ready to do this (the DMA thing really is a nice side
effect, I mostly wanted it for 32on64, so that I can restrict domain
allocations for 32-bit domains). Are you saying I should throw away the
DMA specialization then altogether (I already have no special DMA heap
anymore)? The leftovers from it are so that one can reserve some portion
of low memory to be returned only when the width restriction is low enough
(i.e. to retain dma_emergency_pool functionality), which certainly isn't
really appropriate anymore now (it should rather be a percentage or
something like that, so that the lower you get the more of the memory
remains reserved for specialized allocations).

Jan

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