Re: [PATCH 2/4] arm64: defconfig: Set cma heap size to 128MB

[Thierry Reding]

On Fri, Aug 19, 2016 at 11:42:06PM +0800, Guodong Xu wrote:
> From: Xinliang Liu <xinliang.liu@xxxxxxxxxx>
> 
> For debian linux, cma heap is used to allocate graphic buffers.
> The default size is 16 MB which is not enought.
> So increase the size to 128 MB.
> 
> Signed-off-by: Xinliang Liu <xinliang.liu@xxxxxxxxxx>
> ---
>  arch/arm64/configs/defconfig | 1 +
>  1 file changed, 1 insertion(+)

This is a bad idea. You're increasing this heap for all users of the
default configuration (which on 64-bit ARM is everyone, really). Many of
the devices don't require the CMA except maybe for the occasional very
small buffer. Most implement some form of IOMMU support that removes the
need for large amounts of contiguous physical memory.

I think it's a better idea to have some bootloader append a cma=128 to
the kernel command-line if necessary.

Thierry

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