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

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Date:   Mon, 10 Apr 2023 18:02:41 +0800
From:   "chenjiahao (C)" <chenjiahao16@...wei.com>
To:     Simon Horman <horms@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        <kexec@...ts.infradead.org>, <linux-doc@...r.kernel.org>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <conor.dooley@...rochip.com>, <guoren@...nel.org>,
        <heiko@...ech.de>, <bjorn@...osinc.com>, <alex@...ti.fr>,
        <akpm@...ux-foundation.org>, <atishp@...osinc.com>,
        <bhe@...hat.com>, <thunder.leizhen@...wei.com>
Subject: Re: [PATCH -next v3 0/2] support allocating crashkernel above 4G
 explicitly on riscv


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