RE: [PATCH] dma: Per-NUMA-node CMA should depend on NUMA

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: hch@xxxxxx [mailto:hch@xxxxxx]
> Sent: Tuesday, October 27, 2020 8:55 PM
> To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx>
> Cc: Robin Murphy <robin.murphy@xxxxxxx>; hch@xxxxxx;
> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] dma: Per-NUMA-node CMA should depend on NUMA
> 
> On Mon, Oct 26, 2020 at 08:07:43PM +0000, Song Bao Hua (Barry Song)
> wrote:
> > > diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> > > index c99de4a21458..964b74c9b7e3 100644
> > > --- a/kernel/dma/Kconfig
> > > +++ b/kernel/dma/Kconfig
> > > @@ -125,7 +125,8 @@ if  DMA_CMA
> > >
> > >  config DMA_PERNUMA_CMA
> > >  	bool "Enable separate DMA Contiguous Memory Area for each NUMA
> > > Node"
> > > -	default NUMA && ARM64
> > > +	depends on NUMA
> > > +	default ARM64
> >
> > On the other hand, at this moment, only ARM64 is calling the init code
> > to get per_numa cma. Do we need to
> > depends on NUMA && ARM64 ?
> > so that this is not enabled by non-arm64?
> 
> I actually hate having arch symbols in common code.  A new
> ARCH_HAS_DMA_PERNUMA_CMA, only selected by arm64 for now would be
> more
> clean I think.

Sounds good to me.

BTW,  +Will.

Last time we talked about default pernuma cma size, you suggested a bootargs
in arch/arm64/Kconfig but Will seems to have different idea. Am I right, Will?

Would we let aarch64 call dma_pernuma_cma_reserve(16MB) rather than
dma_pernuma_cma_reserve()?

In this way, users will at least get a default pernuma CMA which is required
at least by IOMMU. If users set a "cma_pernuma" bootargs, it will overwrite
the default size from aarch64 code?

I mean

- void __init dma_pernuma_cma_reserve(size_t size)
+ void __init dma_pernuma_cma_reserve(size_t size)
{
	if (!pernuma_size_bytes)
+		pernuma_size_bytes = size;
	....
}

Right now, it is easy that users will forget to set cma_pernuma in bootargs.
Probably this feature is not enabled by users.

Thanks
Barry