Re: [PATCH] dma-pool: use single atomic pool for both DMA zones

[Christoph Hellwig]

On Tue, Jul 07, 2020 at 02:28:04PM +0200, Nicolas Saenz Julienne wrote:
> When allocating atomic DMA memory for a device, the dma-pool core
> queries __dma_direct_optimal_gfp_mask() to check which atomic pool to
> use. It turns out the GFP flag returned is only an optimistic guess.
> The pool selected might sometimes live in a zone higher than the
> device's view of memory.
> 
> As there isn't a way to grantee a mapping between a device's DMA
> constraints and correct GFP flags this unifies both DMA atomic pools.
> The resulting pool is allocated in the lower DMA zone available, if any,
> so as for devices to always get accessible memory while having the
> flexibility of using dma_pool_kernel for the non constrained ones.
> 
> Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to map to gfp mask")
> Reported-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> Suggested-by: Robin Murphy <robin.murphy@xxxxxxx>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>

Hmm, this is not what I expected from the previous thread.  I thought
we'd just use one dma pool based on runtime available of the zones..