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

On 2022/2/21 11:48, Baoquan He wrote:

On 01/24/22 at 04:47pm, Zhen Lei wrote:

quoted

From: Chen Zhou <redacted>

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 <redacted>
Signed-off-by: Zhen Lei <redacted>
---
 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).

Hmm, we may not need the details related to crashkernel,high|low in this
section. This just gives examples of basic configation for each ARCH.
The detailed configuration of all crashkernel setting can be found in
"crashkernel syntax" section, I don't think arm64 is so special to need
a specific one.

quoted

 
 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.

How about add ARM64 like below to avoid redundant words?
  			[KNL, X86-64, ARM64] Select a region under 4G first, and
  			fall back to reserve region above 4G when '@offset'
  			hasn't been specified.

I agree very much, and I think that's the right thing to do. Thanks.

I wanted to do the same before, just wasn't sure if the format was correct. I just
looked at the other descriptions in kernel-parameters.txt and found that there are
many precedents.

"movablecore=    [KNL,X86,IA-64,PPC]"

quoted

 
 	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.

Ditto, please don't add redundent words if it's similar to x86_64
handling.

quoted

 	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.

Ditto.

quoted

 	cryptomgr.notests
 			[KNL] Disable crypto self-tests
 
-- 
2.25.1

.

-- 
Regards,
  Zhen Lei

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