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

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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




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