[PATCH v2] dma-pool: don't allocate DMA32 pool if no 32-bit memory

[Robin Murphy]

On 2026-01-12 6:58 am, Vladimir Kondratiev wrote:
> If system have no 32-bit memory, GFP_DMA32 pool allocation will
> obviously fail, so skip it.

Note that the rest of the code doesn't quite work right if 
CONFIG_ZONE_DMA32 is enabled but atomic_pool_dma32 is NULL - seems such 
a setup wasn't really anticipated. Funnily enough, I also recently wrote 
a patch series to improve this more generally, but hadn't got round to 
writing a cover letter yet - lemme finish that up and post it...

Thanks,
Robin.

> Changes in v2: use arch-independent "memblock_start_of_DRAM" to get
> DRAM base address
> 
> Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev at mobileye.com>
> ---
>   kernel/dma/pool.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index ee45dee33d49..ecd77a0272f2 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -209,7 +209,7 @@ static int __init dma_atomic_pool_init(void)
>   		if (!atomic_pool_dma)
>   			ret = -ENOMEM;
>   	}
> -	if (IS_ENABLED(CONFIG_ZONE_DMA32)) {
> +	if (IS_ENABLED(CONFIG_ZONE_DMA32) && memblock_start_of_DRAM() < BIT_ULL(32)) {
>   		atomic_pool_dma32 = __dma_atomic_pool_init(atomic_pool_size,
>   						GFP_KERNEL | GFP_DMA32);
>   		if (!atomic_pool_dma32)
> 
> base-commit: 7d0a66e4bb9081d75c82ec4957c50034cb0ea449