Re: [PATCH v12 7/9] kdump: add threshold for the required memory

[chenzhou]

On 2020/10/6 1:12, Catalin Marinas wrote:
> On Mon, Sep 07, 2020 at 09:47:43PM +0800, Chen Zhou wrote:
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 3f735cb37ace..d11d597a470d 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -378,6 +378,15 @@ int __init reserve_crashkernel_low(void)
>>  }
>>  
>>  #if defined(CONFIG_X86) || defined(CONFIG_ARM64)
>> +
>> +/*
>> + * Add a threshold for required memory size of crashkernel. If required memory
>> + * size is greater than threshold, just go for high allocation directly. The
>> + * value of threshold is set as half of the total low memory.
>> + */
>> +#define REQUIRED_MEMORY_THRESHOLD	(memblock_mem_size(CRASH_ADDR_LOW_MAX >> \
>> +			PAGE_SHIFT) >> 1)
>> +
>>  #ifdef CONFIG_KEXEC_CORE
>>  /*
>>   * reserve_crashkernel() - reserves memory for crash kernel
>> @@ -422,7 +431,7 @@ void __init reserve_crashkernel(void)
>>  		 * So try low memory first and fall back to high memory
>>  		 * unless "crashkernel=size[KMG],high" is specified.
>>  		 */
>> -		if (!high)
>> +		if (!high && crash_size <= REQUIRED_MEMORY_THRESHOLD)
>>  			crash_base = memblock_find_in_range(CRASH_ALIGN,
>>  						CRASH_ADDR_LOW_MAX,
>>  						crash_size, CRASH_ALIGN);
> Since any change now is affecting the x86 semantics slightly, I'd
> suggest you drop this patch. We can add it later if needed, once the
> core changes are in.
Ok, i will drop this patch in next version.

Thanks,
Chen Zhou
>
> Thinking about this, if one requires a crashkernel reservation that
> allocates all of the ZONE_DMA, it would probably be noticed and explicit
> ,high/,low options can be used.
>
> Note that we are also trying to make ZONE_DMA full 32-bit on non-RPi4
> hardware.
>