Subject: Re: [PATCH v12 3/9] x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions reserve_crashkernel[_low]()

From: Baoquan He <[email-masked]>
Date: Fri, 18 Sep 2020 15:25:26 +0800

Hi,

On 09/07/20 at 09:47pm, Chen Zhou wrote:
> To make the functions reserve_crashkernel[_low]() as generic,
> replace some hard-coded numbers with macro CRASH_ADDR_LOW_MAX.
> 
> Signed-off-by: Chen Zhou <[email-masked]>
> ---
>  arch/x86/kernel/setup.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index d7fd90c52dae..71a6a6e7ca5b 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -430,7 +430,7 @@ static int __init reserve_crashkernel_low(void)
>  	unsigned long total_low_mem;
>  	int ret;
>  
> -	total_low_mem = memblock_mem_size(1UL << (32 - PAGE_SHIFT));
> +	total_low_mem = memblock_mem_size(CRASH_ADDR_LOW_MAX >> PAGE_SHIFT);

Just note that the replacement has been done in another patch from Mike
Rapoport, partially. He seems to have done reserve_crashkernel_low()
part, there's one left in reserve_crashkernel(), you might want to check
that. 

Mike's patch which is from a patchset has been merged into Andrew's next
tree.

commit 6e50f7672ffa362e9bd4bc0c0d2524ed872828c5
Author: Mike Rapoport <[email-masked]>
Date:   Wed Aug 26 15:22:32 2020 +1000

    x86/setup: simplify reserve_crashkernel()

>  
>  	/* crashkernel=Y,low */
>  	ret = parse_crashkernel_low(boot_command_line, total_low_mem, &low_size, &base);
> @@ -451,7 +451,7 @@ static int __init reserve_crashkernel_low(void)
>  			return 0;
>  	}
>  
> -	low_base = memblock_find_in_range(CRASH_ALIGN, 1ULL << 32, low_size, CRASH_ALIGN);
> +	low_base = memblock_find_in_range(CRASH_ALIGN, CRASH_ADDR_LOW_MAX, low_size, CRASH_ALIGN);
>  	if (!low_base) {
>  		pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
>  		       (unsigned long)(low_size >> 20));
> @@ -504,8 +504,9 @@ static void __init reserve_crashkernel(void)
>  	if (!crash_base) {
>  		/*
>  		 * Set CRASH_ADDR_LOW_MAX upper bound for crash memory,
> -		 * crashkernel=x,high reserves memory over 4G, also allocates
> -		 * 256M extra low memory for DMA buffers and swiotlb.
> +		 * crashkernel=x,high reserves memory over CRASH_ADDR_LOW_MAX,
> +		 * also allocates 256M extra low memory for DMA buffers
> +		 * and swiotlb.
>  		 * But the extra memory is not required for all machines.
>  		 * So try low memory first and fall back to high memory
>  		 * unless "crashkernel=size[KMG],high" is specified.
> @@ -539,7 +540,7 @@ static void __init reserve_crashkernel(void)
>  		return;
>  	}
>  
> -	if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) {
> +	if (crash_base >= CRASH_ADDR_LOW_MAX && reserve_crashkernel_low()) {
>  		memblock_free(crash_base, crash_size);
>  		return;
>  	}
> -- 
> 2.20.1
> 

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