linux-kernel - Re: [PATCH v21 3/5] arm64: kdump: reimplement crashkernel=X

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Message-ID: <d938a7e8-6b4f-f24d-41d3-8058ca2b2ac8@oracle.com>
Date:   Mon, 21 Mar 2022 09:09:19 -0500
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     John Donnelly <John.p.donnelly@...cle.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org, Dave Young <dyoung@...hat.com>,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>
Subject: Re: [PATCH v21 3/5] arm64: kdump: reimplement crashkernel=X

On 3/21/22 8:29AM, John Donnelly wrote:
> On 2/26/22 9:07 PM, Zhen Lei wrote:
>> From: Chen Zhou <chenzhou10@...wei.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@...wei.com>
>> Co-developed-by: Zhen Lei <thunder.leizhen@...wei.com>
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>