Re: [PATCH v20 3/5] arm64: kdump: reimplement crashkernel=X

[Leizhen (ThunderTown)]

On 2022/2/14 11:52, Baoquan He wrote:
> On 01/24/22 at 04:47pm, Zhen Lei wrote:
> ......
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 6c653a2c7cff052..a5d43feac0d7d96 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -71,6 +71,30 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>  #define CRASH_ADDR_LOW_MAX	arm64_dma_phys_limit
>>  #define CRASH_ADDR_HIGH_MAX	MEMBLOCK_ALLOC_ACCESSIBLE
>>  
>> +static int __init reserve_crashkernel_low(unsigned long long low_size)
>> +{
>> +	unsigned long long low_base;
>> +
>> +	/* passed with crashkernel=0,low ? */
>> +	if (!low_size)
>> +		return 0;
>> +
>> +	low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
>> +	if (!low_base) {
>> +		pr_err("cannot allocate crashkernel low memory (size:0x%llx).\n", low_size);
>> +		return -ENOMEM;
>> +	}
>> +
>> +	pr_info("crashkernel low memory reserved: 0x%llx - 0x%llx (%lld MB)\n",
>> +		low_base, low_base + low_size, low_size >> 20);
>> +
>> +	crashk_low_res.start = low_base;
>> +	crashk_low_res.end   = low_base + low_size - 1;
>> +	insert_resource(&iomem_resource, &crashk_low_res);
>> +
>> +	return 0;
>> +}
>> +
>>  /*
>>   * reserve_crashkernel() - reserves memory for crash kernel
> 
> My another concern is the crashkernel=,low handling. In this patch, the
> code related to low memory is obscure. Wondering if we should make them
> explicit with a little redundant but very clear code flows. Saying this
> because the code must be very clear to you and reviewers, it may be
> harder for later code reader or anyone interested to understand.
> 
> 1) crashkernel=X,high
> 2) crashkernel=X,high crashkernel=Y,low
> 3) crashkernel=X,high crashkernel=0,low
> 4) crashkernel=X,high crashkernel='messy code',low
> 5) crashkernel=X //fall back to high memory, low memory is required then.
> 
> It could be me thinking about it too much. I made changes to your patch
> with a tuning, not sure if it's OK to you. Otherwise, this patchset

I think it's good.

> works very well for all above test cases, it's ripe to be merged for
> wider testing.

I will test it tomorrow. I've prepared a little more use cases than yours.

1) crashkernel=4G						//high=4G, low=256M
2) crashkernel=4G crashkernel=512M,high crashkernel=512M,low	//high=4G, low=256M, high and low are ignored
3) crashkernel=4G crashkernel=512M,high				//high=4G, low=256M, high is ignored
4) crashkernel=4G crashkernel=512M,low				//high=4G, low=256M, low is ignored
5) crashkernel=4G@0xe0000000					//high=0G, low=0M, cannot allocate, failed
6) crashkernel=512M						//high=0G, low=512M
7) crashkernel=128M						//high=0G, low=128M
8) crashkernel=512M@0xde000000		//512M@3552M		//high=0G, low=512M
9) crashkernel=4G,high						//high=4G, low=256M
a) crashkernel=4G,high crashkernel=512M,low			//high=4G, low=512M
b) crashkernel=512M,high crashkernel=128M,low			//high=512M, low=128M
c) crashkernel=512M,low						//high=0G, low=0M, invalid


> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index a5d43feac0d7..671862c56d7d 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -94,7 +94,8 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>  
>  	return 0;
>  }
> -
> +/*Words explaining why it's 256M*/
> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE SZ_256M
>  /*
>   * reserve_crashkernel() - reserves memory for crash kernel
>   *
> @@ -105,10 +106,10 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>  static void __init reserve_crashkernel(void)
>  {
>  	unsigned long long crash_base, crash_size;
> -	unsigned long long crash_low_size = SZ_256M;
> +	unsigned long long crash_low_size;
>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>  	int ret;
> -	bool fixed_base;
> +	bool fixed_base, high;
>  	char *cmdline = boot_command_line;
>  
>  	/* crashkernel=X[@offset] */
> @@ -126,7 +127,10 @@ static void __init reserve_crashkernel(void)
>  		ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
>  		if (!ret)
>  			crash_low_size = low_size;
> +		else
> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>  
> +		high = true;
>  		crash_max = CRASH_ADDR_HIGH_MAX;
>  	}
>  
> @@ -134,7 +138,7 @@ static void __init reserve_crashkernel(void)
>  	crash_size = PAGE_ALIGN(crash_size);
>  
>  	/* User specifies base address explicitly. */
> -	if (crash_base)
> +	if (fixed_base)
>  		crash_max = crash_base + crash_size;
>  
>  retry:
> @@ -156,7 +160,10 @@ static void __init reserve_crashkernel(void)
>  		return;
>  	}
>  
> -	if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
> +	if (crash_base >= SZ_4G && !high) 
> +		crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +
> +	if (reserve_crashkernel_low(crash_low_size)) {
>  		memblock_phys_free(crash_base, crash_size);
>  		return;
>  	}

It feels like {} may need to be added here so that it is in branch "if (crash_base >= SZ_4G)".
The case of "crashkernel=128M" will not fall back to high memory and does not need to reserve
low memory again.

> 
>>   *
>> @@ -81,29 +105,62 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>  static void __init reserve_crashkernel(void)
>>  {
>>  	unsigned long long crash_base, crash_size;
>> +	unsigned long long crash_low_size = SZ_256M;
>>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>  	int ret;
>> +	bool fixed_base;
>> +	char *cmdline = boot_command_line;
>>  
>> -	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>> +	/* crashkernel=X[@offset] */
>> +	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>>  				&crash_size, &crash_base);
>> -	/* no crashkernel= or invalid value specified */
>> -	if (ret || !crash_size)
>> -		return;
>> +	if (ret || !crash_size) {
>> +		unsigned long long low_size;
>>  
>> +		/* crashkernel=X,high */
>> +		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>> +		if (ret || !crash_size)
>> +			return;
>> +
>> +		/* crashkernel=X,low */
>> +		ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
>> +		if (!ret)
>> +			crash_low_size = low_size;
>> +
>> +		crash_max = CRASH_ADDR_HIGH_MAX;
>> +	}
>> +
>> +	fixed_base = !!crash_base;
>>  	crash_size = PAGE_ALIGN(crash_size);
>>  
>>  	/* User specifies base address explicitly. */
>>  	if (crash_base)
>>  		crash_max = crash_base + crash_size;
>>  
>> +retry:
>>  	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>>  					       crash_base, crash_max);
>>  	if (!crash_base) {
>> +		/*
>> +		 * Attempt to fully allocate low memory failed, fall back
>> +		 * to high memory, the minimum required low memory will be
>> +		 * reserved later.
>> +		 */
>> +		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
>> +			crash_max = CRASH_ADDR_HIGH_MAX;
>> +			goto retry;
>> +		}
>> +
>>  		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>>  			crash_size);
>>  		return;
>>  	}
>>  
>> +	if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
>> +		memblock_phys_free(crash_base, crash_size);
>> +		return;
>> +	}
>> +
>>  	pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
>>  		crash_base, crash_base + crash_size, crash_size >> 20);
>>  
>> @@ -112,6 +169,9 @@ static void __init reserve_crashkernel(void)
>>  	 * map. Inform kmemleak so that it won't try to access it.
>>  	 */
>>  	kmemleak_ignore_phys(crash_base);
>> +	if (crashk_low_res.end)
>> +		kmemleak_ignore_phys(crashk_low_res.start);
>> +
>>  	crashk_res.start = crash_base;
>>  	crashk_res.end = crash_base + crash_size - 1;
>>  	insert_resource(&iomem_resource, &crashk_res);
>> -- 
>> 2.25.1
>>
> 
> .
> 

-- 
Regards,
  Zhen Lei