Re: [RFC PATCH 04/12] s390/cio: introduce cio DMA pool

Sebastian Ott
2019-04-11T18:25:01Z

On Fri, 5 Apr 2019, Halil Pasic wrote:
> To support protected virtualization cio will need to make sure the
> memory used for communication with the hypervisor is DMA memory.
>
> Let us introduce a DMA pool to cio that will help us in allocating
> deallocating those chunks of memory.
>
> We use a gen_pool backed with DMA pages to avoid each allocation
> effectively wasting a page, as we typically allocate much less
> than PAGE_SIZE.

I don't think we should use this global DMA pool. I guess it's OK for
stuff like airq (where we don't have a struct device at hand) but for
CCW we should use the device we have. Yes, this way we waste some memory
but all dma memory a device uses should fit in a page - so the wastage
is not too much.

Sebastian