Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone

Nicolas Saenz Julienne
2020-08-06T17:23:51Z

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On Thu, 2020-08-06 at 07:18 +0200, Christoph Hellwig wrote:
> On Tue, Aug 04, 2020 at 11:43:15AM +0200, Nicolas Saenz Julienne wrote:
> > > Second I don't see the need (and actually some harm) in preventing GFP_KERNEL
> > > allocations from dipping into lower CMA areas - something that we did support
> > > before 5.8 with the single pool.
> >
> > My thinking is the least we pressure CMA the better, it's generally scarse, and
> > it'll not grow as the atomic pools grow. As far as harm is concerned, we now
> > check addresses for correctness, so we shouldn't run into problems.
> >
> > There is a potential case for architectures defining a default CMA but not
> > defining DMA zones where this could be problematic. But isn't that just plain
> > abusing CMA? If you need low memory allocations, you should be defining DMA
> > zones.
>
> The latter is pretty much what I expect, as we only support the default and
> per-device DMA CMAs.

Fair enough, should I send a v3 with everything cleaned-up/rebased, or you'd
rather pick it up from your version?

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