Re: [PATCH v11 5/5] kdump: update Documentation about crashkernel
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2020-09-02 17:13:52
Also in:
kexec, linux-arm-kernel, lkml
On Sat, Aug 01, 2020 at 09:08:56PM +0800, Chen Zhou wrote:
quoted hunk ↗ jump to hunk
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.
+ 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).
-- Catalin