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Date:   Mon, 21 Mar 2022 09:09:19 -0500
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Subject: Re: [PATCH v21 3/5] arm64: kdump: reimplement crashkernel=X
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To:     John Donnelly <John.p.donnelly@oracle.com>,
        Zhen Lei <thunder.leizhen@huawei.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org, Dave Young <dyoung@redhat.com>,
        Baoquan He <bhe@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        kexec@lists.infradead.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        devicetree@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        linux-doc@vger.kernel.org
Cc:     Randy Dunlap <rdunlap@infradead.org>,
        Feng Zhou <zhoufeng.zf@bytedance.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Chen Zhou <dingguo.cz@antgroup.com>
References: <20220227030717.1464-1-thunder.leizhen@huawei.com>
 <20220227030717.1464-4-thunder.leizhen@huawei.com>
 <cc0186d9-29a3-8eff-e38a-95fd4dd9c46f@oracle.com>
From:   Dave Kleikamp <dave.kleikamp@oracle.com>
In-Reply-To: <cc0186d9-29a3-8eff-e38a-95fd4dd9c46f@oracle.com>
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On 3/21/22 8:29AM, John Donnelly wrote:
> On 2/26/22 9:07 PM, Zhen Lei wrote:
>> From: Chen Zhou <chenzhou10@huawei.com>
>>
>> There are following issues in arm64 kdump:
>> 1. We use crashkernel=X to reserve crashkernel below 4G, which
>> will fail when there is no enough low memory.
> 
>                          " Not enough "
>> 2. If reserving crashkernel above 4G, in this case, crash dump
>> kernel will boot failure because there is no low memory available
>> for allocation.
> 
>   We can't have a "boot failure". If the requested reservation
>   can not be met,  the kdump  configuration is not setup.

I think you misread this. Without these patches, if only high memory is 
reserved for the crash kernel, then the crash kernel will fail to boot.

>>
>> To solve these issues, change the behavior of crashkernel=X and
>> introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
>> in DMA zone, and fall back to high allocation if it fails.
>> We can also use "crashkernel=X,high" to select a region above DMA zone,
>> which also tries to allocate at least 256M in DMA zone automatically.
>> "crashkernel=Y,low" can be used to allocate specified size low memory.
> 
> Is there going to be documentation on what values certain Arm platforms 
> are going to use this on ?
> 
>>
>> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
>> Co-developed-by: Zhen Lei <thunder.leizhen@huawei.com>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>