[patch 7/7] Add documentation for extended crashkernel syntax

[Bernhard Walle <bwalle@suse.de>]

This adds the documentation for the extended crashkernel syntax into
Documentation/kdump/kdump.txt.

Signed-off-by: Bernhard Walle <bwalle@suse.de>

---
 Documentation/kdump/kdump.txt       |   26 ++++++++++++++++++++++++++
 Documentation/kernel-parameters.txt |    7 +++++++
 2 files changed, 33 insertions(+)

--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -231,6 +231,32 @@ Dump-capture kernel config options (Arch
   any space below the alignment point will be wasted.
 
 
+Extended crashkernel syntax
+===========================
+
+While the "crashkernel=size[@offset]" syntax is sufficient for most
+configurations, sometimes it's handy to have the reserved memory dependent
+on the value of System RAM -- that's mostly for distributors that pre-setup
+the kernel command line to avoid a unbootable system after some memory has
+been removed from the machine.
+
+The syntax is:
+
+    crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
+    range=start-[end]
+
+For example:
+
+    crashkernel=512M-2G:64M,2G-:128M
+
+This would mean:
+
+    1) if the RAM is smaller than 512M, then don't reserve anything
+       (this is the "rescue" case)
+    2) if the RAM size is between 512M and 2G, then reserve 64M
+    3) if the RAM size is larger than 2G, then reserve 128M
+
+
 Boot into System Kernel
 =======================
 
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -495,6 +495,13 @@ and is between 256 and 4096 characters. 
 			[KNL] Reserve a chunk of physical memory to
 			hold a kernel to switch to with kexec on panic.
 
+	crashkernel=range1:size1[,range2:size2,...][@offset]
+			[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.
+
 	cs4232=		[HW,OSS]
 			Format: <io>,<irq>,<dma>,<dma2>,<mpuio>,<mpuirq>
 

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