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Subject: Re: [PATCH v9 5/5] kdump: update Documentation about crashkernel on
 arm64
To:     Dave Young <dyoung@redhat.com>
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From:   chenzhou <chenzhou10@huawei.com>
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Date:   Fri, 3 Jul 2020 08:57:34 +0800
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Hi Dave,


On 2020/7/2 10:59, Dave Young wrote:
> Hi Chen,
> On 06/28/20 at 04:34pm, Chen Zhou wrote:
>> Now we support crashkernel=X,[low] on arm64, update the Documentation.
>> We could use parameters "crashkernel=X crashkernel=Y,low" to reserve
>> memory above 4G.
>>
>> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
>> Tested-by: John Donnelly <John.p.donnelly@oracle.com>
>> Tested-by: Prabhakar Kushwaha <pkushwaha@marvell.com>
>> ---
>>  Documentation/admin-guide/kdump/kdump.rst       | 13 +++++++++++--
>>  Documentation/admin-guide/kernel-parameters.txt | 17 +++++++++++++++--
>>  2 files changed, 26 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
>> index 2da65fef2a1c..6ba294d425c9 100644
>> --- a/Documentation/admin-guide/kdump/kdump.rst
>> +++ b/Documentation/admin-guide/kdump/kdump.rst
>> @@ -299,7 +299,13 @@ Boot into System Kernel
>>     "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
>>     starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
>>  
>> -   On x86 and x86_64, use "crashkernel=64M@16M".
>> +   On x86 use "crashkernel=64M@16M".
>> +
>> +   On x86_64, use "crashkernel=Y[@X]" to select a region under 4G first, and
>> +   fall back to reserve region above 4G when '@offset' hasn't been specified.
> Actually crashkernel=Y without the offset works well, I do not see why
> we need the offset, it should be some legacy thing.  So it should be
> better just use the Y without offset here, and just leave a note
> somewhere people can use [@X] offset when they really have to.
>
>> +   We can also use "crashkernel=X,high" to select a region above 4G, which
>> +   also tries to allocate at least 256M below 4G automatically and
>> +   "crashkernel=Y,low" can be used to allocate specified size low memory.
>>  
>>     On ppc64, use "crashkernel=128M@32M".
>>  
>> @@ -316,8 +322,11 @@ Boot into System Kernel
>>     kernel will automatically locate the crash kernel image within the
>>     first 512MB of RAM if X is not given.
>>  
>> -   On arm64, use "crashkernel=Y[@X]".  Note that the start address of
>> +   On arm64, use "crashkernel=Y[@X]". Note that the start address of
>>     the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
>> +   If crashkernel=Z,low is specified simultaneously, reserve spcified size
>> +   low memory for crash kdump kernel devices firstly and then reserve memory
> "devices" seems not very accurate, maybe just drop the "for crash kdump
> kernel devices" since it is clear based on the context.
>
>> +   above 4G.
>>  
>>  Load the Dump-capture Kernel
>>  ============================
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index fb95fad81c79..335431a351c0 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -722,6 +722,9 @@
>>  			[KNL, x86_64] select a region under 4G first, and
>>  			fall back to reserve region above 4G when '@offset'
>>  			hasn't been specified.
>> +			[KNL, arm64] If crashkernel=X,low is specified, reserve
>> +			spcified size low memory for crash kdump kernel devices
> Ditto.
>
>> +			firstly, and then reserve memory above 4G.
>>  			See Documentation/admin-guide/kdump/kdump.rst for further details.
>>  
>>  	crashkernel=range1:size1[,range2:size2,...][@offset]
>> @@ -746,13 +749,23 @@
>>  			requires at least 64M+32K low memory, also enough extra
>>  			low memory is needed to make sure DMA buffers for 32-bit
>>  			devices won't run out. Kernel would try to allocate at
>> -			at least 256M below 4G automatically.
>> +			least 256M below 4G automatically.
>>  			This one let user to specify own low range under 4G
>>  			for second kernel instead.
>>  			0: to disable low allocation.
>>  			It will be ignored when crashkernel=X,high is not used
>>  			or memory reserved is below 4G.
>> -
>> +			[KNL, arm64] range under 4G.
>> +			This one let user to specify own low range under 4G
>> +			for crash dump kernel instead.
>> +			Different with x86_64, kernel allocates specified size
> sounds better:
> s/Different with/Be different from
>
> s/allocates/reserves
>
>> +			physical memory region only when this parameter is specified
>> +			instead of trying to allocate at least 256M below 4G
> s/allocate/reserve
>
>> +			automatically.
>> +			This parameter is used along with crashkernel=X when we
> Could change the passive sentence to below:
> "Use this parameter along with"
Thanks for your review and suggestions. I will update these in next version.

Thanks,
Chen Zhou
>> +			want to reserve crashkernel above 4G. If there are devices
>> +			need to use ZONE_DMA in crash dump kernel, it is also
>> +			a good choice.
>>  	cryptomgr.notests
>>  			[KNL] Disable crypto self-tests
>>  
>> -- 
>> 2.20.1
>>
>>
>> _______________________________________________
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>> http://lists.infradead.org/mailman/listinfo/kexec
>>
> Thanks
> Dave
>
>
> .
>