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

[chenjiahao (C)]

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