Subject: Re: [PATCH v2 14/17] x86/setup: simplify reserve_crashkernel()

From: Baoquan He <[email-masked]>
Date: Wed, 5 Aug 2020 14:00:06 +0800

On 08/02/20 at 07:35pm, Mike Rapoport wrote:
> From: Mike Rapoport <[email-masked]>
> 
> * Replace magic numbers with defines
> * Replace memblock_find_in_range() + memblock_reserve() with
>   memblock_phys_alloc_range()
> * Stop checking for low memory size in reserve_crashkernel_low(). The
>   allocation from limited range will anyway fail if there is no enough
>   memory, so there is no need for extra traversal of memblock.memory
> 
> Signed-off-by: Mike Rapoport <[email-masked]>
> ---
>  arch/x86/kernel/setup.c | 40 ++++++++++++++--------------------------
>  1 file changed, 14 insertions(+), 26 deletions(-)

Applied this patch on top of 5.8, crashkernel reservation works well.
And the code change looks good.

Reviewed-by: Baoquan He <[email-masked]>

> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index d8de4053c5e8..d7ced6982524 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -419,13 +419,13 @@ static int __init reserve_crashkernel_low(void)
>  {
>  #ifdef CONFIG_X86_64
>  	unsigned long long base, low_base = 0, low_size = 0;
> -	unsigned long total_low_mem;
> +	unsigned long low_mem_limit;
>  	int ret;
>  
> -	total_low_mem = memblock_mem_size(1UL << (32 - PAGE_SHIFT));
> +	low_mem_limit = min(memblock_phys_mem_size(), CRASH_ADDR_LOW_MAX);
>  
>  	/* crashkernel=Y,low */
> -	ret = parse_crashkernel_low(boot_command_line, total_low_mem, &low_size, &base);
> +	ret = parse_crashkernel_low(boot_command_line, low_mem_limit, &low_size, &base);
>  	if (ret) {
>  		/*
>  		 * two parts from kernel/dma/swiotlb.c:
> @@ -443,23 +443,17 @@ static int __init reserve_crashkernel_low(void)
>  			return 0;
>  	}
>  
> -	low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN);
> +	low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
>  	if (!low_base) {
>  		pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
>  		       (unsigned long)(low_size >> 20));
>  		return -ENOMEM;
>  	}
>  
> -	ret = memblock_reserve(low_base, low_size);
> -	if (ret) {
> -		pr_err("%s: Error reserving crashkernel low memblock.\n", __func__);
> -		return ret;
> -	}
> -
> -	pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (System low RAM: %ldMB)\n",
> +	pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (low RAM limit: %ldMB)\n",
>  		(unsigned long)(low_size >> 20),
>  		(unsigned long)(low_base >> 20),
> -		(unsigned long)(total_low_mem >> 20));
> +		(unsigned long)(low_mem_limit >> 20));
>  
>  	crashk_low_res.start = low_base;
>  	crashk_low_res.end   = low_base + low_size - 1;
> @@ -503,13 +497,13 @@ static void __init reserve_crashkernel(void)
>  		 * unless "crashkernel=size[KMG],high" is specified.
>  		 */
>  		if (!high)
> -			crash_base = memblock_find_in_range(CRASH_ALIGN,
> -						CRASH_ADDR_LOW_MAX,
> -						crash_size, CRASH_ALIGN);
> +			crash_base = memblock_phys_alloc_range(crash_size,
> +						CRASH_ALIGN, CRASH_ALIGN,
> +						CRASH_ADDR_LOW_MAX);
>  		if (!crash_base)
> -			crash_base = memblock_find_in_range(CRASH_ALIGN,
> -						CRASH_ADDR_HIGH_MAX,
> -						crash_size, CRASH_ALIGN);
> +			crash_base = memblock_phys_alloc_range(crash_size,
> +						CRASH_ALIGN, CRASH_ALIGN,
> +						CRASH_ADDR_HIGH_MAX);
>  		if (!crash_base) {
>  			pr_info("crashkernel reservation failed - No suitable area found.\n");
>  			return;
> @@ -517,19 +511,13 @@ static void __init reserve_crashkernel(void)
>  	} else {
>  		unsigned long long start;
>  
> -		start = memblock_find_in_range(crash_base,
> -					       crash_base + crash_size,
> -					       crash_size, 1 << 20);
> +		start = memblock_phys_alloc_range(crash_size, SZ_1M, crash_base,
> +						  crash_base + crash_size);
>  		if (start != crash_base) {
>  			pr_info("crashkernel reservation failed - memory is in use.\n");
>  			return;
>  		}
>  	}
> -	ret = memblock_reserve(crash_base, crash_size);
> -	if (ret) {
> -		pr_err("%s: Error reserving crashkernel memblock.\n", __func__);
> -		return;
> -	}
>  
>  	if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) {
>  		memblock_free(crash_base, crash_size);
> -- 
> 2.26.2
>