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Date:   Fri, 7 Jul 2023 08:53:52 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Chen Jiahao <chenjiahao16@huawei.com>
Cc:     linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        kexec@lists.infradead.org, linux-doc@vger.kernel.org,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        conor.dooley@microchip.com, guoren@kernel.org, heiko@sntech.de,
        bjorn@rivosinc.com, alex@ghiti.fr, akpm@linux-foundation.org,
        atishp@rivosinc.com, thunder.leizhen@huawei.com, horms@kernel.org
Subject: Re: [PATCH -next v7 0/2] support allocating crashkernel above 4G
 explicitly on riscv
Message-ID: <ZKdiIGRAQYx9zILj@MiWiFi-R3L-srv>
References: <20230704212327.1687310-1-chenjiahao16@huawei.com>
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In-Reply-To: <20230704212327.1687310-1-chenjiahao16@huawei.com>
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On 07/04/23 at 09:23pm, 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
> 
> Following test cases have been performed as expected:
> 1) crashkernel=256M                          //low=256M
> 2) crashkernel=1G                            //low=1G
> 3) crashkernel=4G                            //high=4G, low=128M(default)
> 4) crashkernel=4G crashkernel=256M,high      //high=4G, low=128M(default), high is ignored
> 5) crashkernel=4G crashkernel=256M,low       //high=4G, low=128M(default), low is ignored
> 6) crashkernel=4G,high                       //high=4G, low=128M(default)
> 7) crashkernel=256M,low                      //low=0M, invalid
> 8) crashkernel=4G,high crashkernel=256M,low  //high=4G, low=256M
> 9) crashkernel=4G,high crashkernel=4G,low    //high=0M, low=0M, invalid
> 10) crashkernel=512M@0xd0000000              //low=512M
> 11) crashkernel=1G,high crashkernel=0M,low   //high=1G, low=0M

The series looks good to me, thanks.

Acked-by: Baoquan He <bhe@redhat.com>