On 2021/2/18 16:40, Baoquan He wrote:

On 01/30/21 at 03:10pm, Chen Zhou wrote:

quoted

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.

Nice document adding which also takes care of x86 code implementation,
thanks. By the way, maybe you can remove John's 'Tested-by' since it
doesn't make much sense to test a document patch.

I will remove the Tested-by in next version.

Acked-by: Baoquan He <bhe@redhat.com>

quoted

Signed-off-by: Chen Zhou <redacted>
Tested-by: John Donnelly <redacted>
---
 Documentation/admin-guide/kdump/kdump.rst     | 22 ++++++++++++++++---
 .../admin-guide/kernel-parameters.txt         | 11 ++++++++--
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index 75a9dd98e76e..0877c76f8015 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst

@@ -299,7 +299,16 @@ 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. And go for high allocation
+   directly if the required size is too large.
+   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 +325,15 @@ 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 a10b545c2070..908e5c8b61ba 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt

@@ -738,6 +738,9 @@
 			[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]

@@ -754,6 +757,8 @@
 			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

@@ -762,13 +767,15 @@
 			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
 

-- 
2.20.1

.

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