Re: [PATCH v2] mm: cma: indefinitely retry allocations in cma_alloc

Christoph Hellwig
2020-09-28T07:39:22Z

On Tue, Sep 15, 2020 at 09:53:30AM +0200, David Hildenbrand wrote:
> Two thoughts:
>
> 1. Most (all?) alloc_contig_range() users are interested in handling
> short-term pinnings in a nice way (IOW, make the allocation succeed).
> I'd much rather want to see this being handled in a nice fashion inside
> alloc_contig_range() than having to encode endless loops in the caller.
> This means I strongly prefer something like [3] if feasible. But I can
> understand that stuff ([5]) is complicated. I have to admit that I am
> not an expert on the short term pinning described by you, and how to
> eventually fix it.

Agreed. Also retrying forever is simply broken, and will lead to
deadlocks for the DMA calls into CMA, so with my dma-mapping hat on
I have to hard-NAK this approach.