Re: [PATCH v20 5/5] kdump: update Documentation about crashkernel

[john.p.donnelly@oracle.com]

On 1/24/22 2:47 AM, Zhen Lei wrote:
> From: Chen Zhou <chenzhou10@huawei.com>
> 
> For arm64, the behavior of crashkernel=X has been changed, which
> 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 high region above
> DMA zone, which also tries to allocate at least 256M low memory in
> DMA zone automatically and "crashkernel=Y,low" can be used to allocate
> specified size low memory.
> 
> So update the Documentation.
> 
> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>

Acked-by: John Donnelly  <john.p.donnelly@oracle.com>

> ---
>   Documentation/admin-guide/kdump/kdump.rst       | 11 +++++++++--
>   Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++--
>   2 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index cb30ca3df27c9b2..d4c287044be0c70 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -361,8 +361,15 @@ 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
> -   the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
> +   On arm64, use "crashkernel=X" to try low allocation in DMA zone and
> +   fall back to high allocation if it fails.
> +   We can also use "crashkernel=X,high" to select a high region above
> +   DMA zone, which also tries to allocate at least 256M low memory in
> +   DMA zone automatically.
> +   "crashkernel=Y,low" can be used to allocate specified size low memory.
> +   Use "crashkernel=Y@X" if you really have to reserve memory from
> +   specified start address X. Note that the start address of the kernel,
> +   X if explicitly specified, must be aligned to 2MiB (0x200000).
>   
>   Load the Dump-capture Kernel
>   ============================
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f5a27f067db9ed9..65780c2ca830be0 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -792,6 +792,9 @@
>   			[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] Try low allocation in DMA zone and fall back
> +			to high allocation if it fails when '@offset' hasn't been
> +			specified.
>   			See Documentation/admin-guide/kdump/kdump.rst for further details.
>   
>   	crashkernel=range1:size1[,range2:size2,...][@offset]
> @@ -808,6 +811,8 @@
>   			Otherwise memory region will be allocated below 4G, if
>   			available.
>   			It will be ignored if crashkernel=X is specified.
> +			[KNL, ARM64] range in high memory.
> +			Allow kernel to allocate physical memory region from top.
>   	crashkernel=size[KMG],low
>   			[KNL, X86-64] range under 4G. When crashkernel=X,high
>   			is passed, kernel could allocate physical memory region
> @@ -816,13 +821,15 @@
>   			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 in low memory.
> +			This one let user to specify a low range in DMA zone for
> +			crash dump kernel.
>   	cryptomgr.notests
>   			[KNL] Disable crypto self-tests
>