Re: [PATCH 1/2] memblock tests: model the low allocation limit within dummy memory

[Mike Rapoport <rppt@kernel.org>]

On Sun, Sep 06, 2026 at 10:40:10PM +0800, Tianyi Chen wrote:
> The simulator represents physical addresses using the address of its
> allocated buffer. That buffer can lie above the default
> ARCH_LOW_ADDRESS_LIMIT, preventing meaningful memblock_alloc_low()
> tests.
> 
> Use the existing architecture override in asm/dma.h to place the limit
> halfway through the dummy memory buffer. Resolve it after the buffer
> has been allocated, so both low and high memory can be represented
> regardless of its address. The production allocator is unchanged.
> 
> Assisted-by: LLM

Please add LLM attribution as per 

https://docs.kernel.org/process/coding-assistants.html#attribution

> Signed-off-by: Tianyi Chen <hi@tychen.cc>
> ---
>  tools/testing/memblock/asm/dma.h      | 6 ++++++
>  tools/testing/memblock/tests/common.c | 5 +++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/tools/testing/memblock/asm/dma.h b/tools/testing/memblock/asm/dma.h
> index 13ff8e5d22e..6607408dcf2 100644
> --- a/tools/testing/memblock/asm/dma.h
> +++ b/tools/testing/memblock/asm/dma.h
> @@ -2,4 +2,10 @@
>  #ifndef _TOOLS_DMA_H
>  #define _TOOLS_DMA_H
>  
> +#include <linux/types.h>
> +
> +phys_addr_t dummy_physical_memory_low_limit(void);
> +
> +#define ARCH_LOW_ADDRESS_LIMIT dummy_physical_memory_low_limit()
> +
>  #endif
> diff --git a/tools/testing/memblock/tests/common.c b/tools/testing/memblock/tests/common.c
> index 3250c8e5124..4e6a920c459 100644
> --- a/tools/testing/memblock/tests/common.c
> +++ b/tools/testing/memblock/tests/common.c
> @@ -118,6 +118,11 @@ phys_addr_t dummy_physical_memory_base(void)
>  	return (phys_addr_t)memory_block.base;
>  }
>  
> +phys_addr_t dummy_physical_memory_low_limit(void)
> +{
> +	return dummy_physical_memory_base() + MEM_SIZE / 2;

Shouldn't this be PHYS_MEM_SIZE?

> +}
> +
>  static void usage(const char *prog)
>  {
>  	BUILD_BUG_ON(ARRAY_SIZE(help_opts) != ARRAY_SIZE(long_opts) - 1);
> -- 
> 2.55.0
> 
> 

-- 
Sincerely yours,
Mike.