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SubjectRe: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love
On Fri, Apr 27, 2018 at 09:18:43AM +0200, Michal Hocko wrote:
> > On Thu, Apr 26, 2018 at 09:54:06PM +0000, Luis R. Rodriguez wrote:
> > > In practice if you don't have a floppy device on x86, you don't need ZONE_DMA,
> >
> > I call BS on that, and you actually explain later why it it BS due
> > to some drivers using it more explicitly. But even more importantly
> > we have plenty driver using it through dma_alloc_* and a small DMA
> > mask, and they are in use - we actually had a 4.16 regression due to
> > them.
>
> Well, but do we need a zone for that purpose? The idea was to actually
> replace the zone by a CMA pool (at least on x86). With the current
> implementation of the CMA we would move the range [0-16M] pfn range into
> zone_movable so it can be used and we would get rid of all of the
> overhead each zone brings (a bit in page flags, kmalloc caches and who
> knows what else)

That wasn't clear in the mail. But if we have anothr way to allocate
<16MB memory we don't need ZONE_DMA for the floppy driver either, so the
above conclusion is still wrong.

> --
> Michal Hocko
> SUSE Labs
---end quoted text---

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