Re: [PATCH -next v3 0/2] support allocating crashkernel above 4G explicitly on riscv

["chenjiahao (C)" <chenjiahao16@huawei.com>]

On 2023/4/7 20:05, Simon Horman wrote:
> On Fri, Apr 07, 2023 at 06:02:04AM +0800, Chen Jiahao wrote:
>> On riscv, the current crash kernel allocation logic is trying to
>> allocate within 32bit addressible memory region by default, if
>> failed, try to allocate without 4G restriction.
>>
>> In need of saving DMA zone memory while allocating a relatively large
>> crash kernel region, allocating the reserved memory top down in
>> high memory, without overlapping the DMA zone, is a mature solution.
>> Hence this patchset introduces the parameter option crashkernel=X,[high,low].
>>
>> One can reserve the crash kernel from high memory above DMA zone range
>> by explicitly passing "crashkernel=X,high"; or reserve a memory range
>> below 4G with "crashkernel=X,low". Besides, there are few rules need
>> to take notice:
>> 1. "crashkernel=X,[high,low]" will be ignored if "crashkernel=size"
>>     is specified.
>> 2. "crashkernel=X,low" is valid only when "crashkernel=X,high" is passed
>>     and there is enough memory to be allocated under 4G.
>> 3. When allocating crashkernel above 4G and no "crashkernel=X,low" is
>>     specified, a 128M low memory will be allocated automatically for
>>     swiotlb bounce buffer.
>> See Documentation/admin-guide/kernel-parameters.txt for more information.
>>
>> To verify loading the crashkernel, adapted kexec-tools is attached below:
>> https://github.com/chenjh005/kexec-tools/tree/build-test-riscv-v2
> Are you planning to submit the kexec-tools patches too?

Yes, but current adaptation is a little informal. I will submit them 
later after further tests.


BR,

Jiahao