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    SubjectRe: [PATCH v11 5/5] kdump: update Documentation about crashkernel
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    On 2020/9/3 1:13, Catalin Marinas wrote:
    > On Sat, Aug 01, 2020 at 09:08:56PM +0800, Chen Zhou wrote:
    >> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
    >> index 2da65fef2a1c..4b58f97351d5 100644
    >> --- a/Documentation/admin-guide/kdump/kdump.rst
    >> +++ b/Documentation/admin-guide/kdump/kdump.rst
    >> @@ -299,7 +299,15 @@ 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=X" to select a region under 4G first, and
    >> + fall back to reserve region above 4G.
    >> + 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.
    >> + Use "crashkernel=Y@X" if you really have to reserve memory from specified
    >> + start address X.
    >>
    >> On ppc64, use "crashkernel=128M@32M".
    >>
    >> @@ -316,8 +324,15 @@ 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 ZONE_DMA, and
    >> + fall back to high allocation if it fails. And go for high allocation
    >> + directly if the required size is too large. If crash_base is outside
    > I wouldn't mention crash_base in the admin guide. That's an
    > implementation detail really and admins are not supposed to read the
    > source code to make sense of the documentation. ZONE_DMA is also a
    > kernel internal, so you'd need to define what it is for arm64. At least
    > the DMA and DMA32 zones are printed during kernel boot.
    Ok, i will fix this in next version.
    >
    >> + ZONE_DMA, try to allocate at least 256M in ZONE_DMA automatically.
    >> + "crashkernel=Y,low" can be used to allocate specified size low memory.
    >> + For non-RPi4 platforms, change ZONE_DMA memtioned above to ZONE_DMA32.
    >> + 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).


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