[PATCH 5/5] kexec: update documentation
v.mayatskih at gmail.com
Thu Apr 22 12:23:12 EDT 2010
Mention new crashkernel= syntax in documentation.
Signed-off-by: Vitaly Mayatskikh <v.mayatskih at gmail.com>
Documentation/kdump/kdump.txt | 40 +++++++++++++++++++++++++++++++++++
Documentation/kernel-parameters.txt | 19 +++++++++++-----
2 files changed, 53 insertions(+), 6 deletions(-)
diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index cab61d8..9f93d17 100644
@@ -266,7 +266,47 @@ This would mean:
2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
3) if the RAM size is larger than 2G, then reserve 128M
+Avoiding memory reservation problem on large systems
+For large systems with huge amount of memory dump-capture kernel
+requires more memory to handle properly old kernel's pages. However,
+it raises issues with h/w-dependent limitations on some platforms. For
+example, on x86-64 system kernel and initrd still have to be placed in
+first 2 gigabytes, because kernel starts executing in 32-bit mode, and
+kdump purgatory code can jump only to 32-bit signed addresses. This
+limitation is a real problem in cases, when dump-capturing region is
+large and cannot fit in good area. For such cases it's possible to use
+special crashkernel syntax:
+<low> and <high> are memory regions for dump-capture kernel in usual
+crashkernel format (size at offset). For example:
+ crashkernel=64M/1G at 4G
+This would mean to allocate 64M of memory at the lowest valid address
+and to allocate 1G at physical address 4G.
+New syntax for extended format (in case of memory dependent
+ crashkernel=2G-32G:256M,32G-:256M/1G at 0/8G
+This would mean:
+ 1) if the RAM is smaller than 2G, then don't reserve anything
+ 2) if the RAM size is between 2G and 32G (exclusive), then reserve 256M
+ 3) if the RAM size is larger than 32G, then reserve 256M at first suitable
+ address (offset 0 means automatically) and reserve 1G at address 8G
Boot into System Kernel
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e2202e9..5e9f234 100644
@@ -568,16 +568,23 @@ and is between 256 and 4096 characters. It is defined in the file
- [KNL] Reserve a chunk of physical memory to
- hold a kernel to switch to with kexec on panic.
- [KNL] Same as above, but depends on the memory
+ crashkernel= [KNL]
+ Reserve a chunk of physical memory to hold a
+ kernel to switch to with kexec on panic.
+ Same as above, but reserve 2 chunks of
+ physical memory.
+ crashkernel= [KNL]
+ Same as above, but depends on the memory
in the running system. The syntax of range is
start-[end] where start and end are both
a memory unit (amount[KMG]). See also
Documentation/kdump/kdump.txt for a example.
+ Same as above, but reserve 2 chunks of memory.
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