In commit:

  9710f581bb4c ("x86, mm: Let "memmap=" take more entries one time")

... 'memmap=' was changed to adopt multiple, comma delimited values in a
single entry, so update the related description.

In the special case of only specifying size value without an offset,
like memmap=nn[KMG], memmap behaves similarly to mem=nn[KMG], so update
it too here.

Furthermore, for memmap=nn[KMG]$ss[KMG], an escape character needs be added
before '$' for some bootloaders. E.g in grub2, if we specify memmap=100M$5G
as suggested by the documentation, "memmap=100MG" gets passed to the kernel.

Clarify all this.

Signed-off-by: Baoquan He <b...@redhat.com>
Cc: Jonathan Corbet <cor...@lwn.net>
Cc: "Rafael J. Wysocki" <rafael.j.wyso...@intel.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Bjorn Helgaas <bhelg...@google.com>
Cc: Mauro Carvalho Chehab <mche...@kernel.org>
Cc: linux-doc@vger.kernel.org
---
 Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index 986e443..d518144 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2097,6 +2097,12 @@
        memmap=nn[KMG]@ss[KMG]
                        [KNL] Force usage of a specific region of memory.
                        Region of memory to be used is from ss to ss+nn.
+                       If @ss[KMG] is omitted, it equals to mem=nn[KMG]
+                       which limits max address as nn[KMG].
+                       Multiple different options can be put into one entry
+                       with comma delimited to save space:
+                       Example:
+                               memmap=100M@2G,100M#3G,1G!1024G
 
        memmap=nn[KMG]#ss[KMG]
                        [KNL,ACPI] Mark specific memory as ACPI data.
@@ -2109,6 +2115,9 @@
                                 memmap=64K$0x18690000
                                 or
                                 memmap=0x10000$0x18690000
+                       Some bootloaders may need escape character before '$',
+                       like in grub2, otherwise '$' and the following number
+                       will be eaten.
 
        memmap=nn[KMG]!ss[KMG]
                        [KNL,X86] Mark specific memory as protected.
-- 
2.5.5

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