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Subject: Re: [PATCH v12 0/9] support reserving crashkernel above 4G on arm64
 kdump
To:     Bhupesh Sharma <bhsharma@redhat.com>,
        Catalin Marinas <catalin.marinas@arm.com>
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CC:     John Donnelly <john.p.donnelly@oracle.com>,
        Will Deacon <will@kernel.org>,
        James Morse <james.morse@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Ingo Molnar" <mingo@redhat.com>, RuiRui Yang <dyoung@redhat.com>,
        Baoquan He <bhe@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
        Prabhakar Kushwaha <prabhakar.pkin@gmail.com>,
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        Rob Herring <robh+dt@kernel.org>,
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From:   chenzhou <chenzhou10@huawei.com>
Message-ID: <8a050973-2eb6-61ed-9172-dd4fd0909f65@huawei.com>
Date:   Tue, 6 Oct 2020 09:48:06 +0800
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Hi Bhupesh,


On 2020/10/6 1:42, Bhupesh Sharma wrote:
> Hi Catalin, Chen,
>
> On Mon, Oct 5, 2020 at 10:39 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>> On Sat, Sep 12, 2020 at 06:44:29AM -0500, John Donnelly wrote:
>>> On 9/7/20 8:47 AM, Chen Zhou wrote:
>>>> Chen Zhou (9):
>>>>    x86: kdump: move CRASH_ALIGN to 2M
>>>>    x86: kdump: make the lower bound of crash kernel reservation
>>>>      consistent
>>>>    x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions
>>>>      reserve_crashkernel[_low]()
>>>>    x86: kdump: move reserve_crashkernel[_low]() into crash_core.c
>>>>    arm64: kdump: introduce some macroes for crash kernel reservation
>>>>    arm64: kdump: reimplement crashkernel=X
>>>>    kdump: add threshold for the required memory
>>>>    arm64: kdump: add memory for devices by DT property
>>>>      linux,usable-memory-range
>>>>    kdump: update Documentation about crashkernel
>> [...]
>>> I did a brief unit-test on 5.9-rc4.
>>>
>>> Please add:
>>>
>>> Tested-by:  John Donnelly <John.p.donnelly@oracle.com>
>> Thanks for testing.
>>
>>> This activity is over a year old. It needs accepted.
>> It's getting there, hopefully in 5.11. There are some minor tweaks to
>> address.
> I think my earlier email with the test results on this series bounced
> off the mailing list server (for some weird reason), but I still see
> several issues with this patchset. I will add specific issues in the
> review comments for each patch again, but overall, with a crashkernel
> size of say 786M, I see the following issue:
>
> # cat /proc/cmdline
> BOOT_IMAGE=(hd7,gpt2)/vmlinuz-5.9.0-rc7+ root=<..snip..>
> rd.lvm.lv=<..snip..> crashkernel=786M
>
> I see two regions of size 786M and 256M reserved in low and high
> regions respectively, So we reserve a total of 1042M of memory, which
> is an incorrect behaviour:
>
> # dmesg | grep -i crash
> [    0.000000] Reserving 256MB of low memory at 2816MB for crashkernel
> (System low RAM: 768MB)
> [    0.000000] Reserving 786MB of memory at 654158MB for crashkernel
> (System RAM: 130816MB)
> [    0.000000] Kernel command line:
> BOOT_IMAGE=(hd2,gpt2)/vmlinuz-5.9.0-rc7+
> root=/dev/mapper/rhel_ampere--hr330a--03-root ro
> rd.lvm.lv=rhel_ampere-hr330a-03/root
> rd.lvm.lv=rhel_ampere-hr330a-03/swap crashkernel=786M cma=1024M
>
> # cat /proc/iomem | grep -i crash
>   b0000000-bfffffff : Crash kernel (low)
>   bfcbe00000-bffcffffff : Crash kernel
>
> IMO, we should test this feature more before including this in 5.11
Thanks for you test. This behavior is what we what. What is the correct behavior you think?

Besides, this feature is been tested by John and PK, and i test for various parameters.
We may miss something, any comments are welcome.

Thanks,
Chen Zhou
>
> Thanks,
> Bhupesh
>
> .
>