x86: add hugepagesz option on 64-bit

Add an hugepagesz=...  option similar to IA64, PPC etc.  to x86-64.

This finally allows to select GB pages for hugetlbfs in x86 now that all
the infrastructure is in place.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 5e20ccb..d55fd88 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -774,8 +774,15 @@
 	hisax=		[HW,ISDN]
 			See Documentation/isdn/README.HiSax.
 
-	hugepages=	[HW,X86-32,IA-64] Maximal number of HugeTLB pages.
-	hugepagesz=	[HW,IA-64,PPC] The size of the HugeTLB pages.
+	hugepages=	[HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
+	hugepagesz=	[HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
+			On x86 this option can be specified multiple times
+			interleaved with hugepages= to reserve huge pages
+			of different sizes. Valid pages sizes on x86-64
+			are 2M (when the CPU supports "pse") and 1G (when the
+			CPU supports the "pdpe1gb" cpuinfo flag)
+			Note that 1GB pages can only be allocated at boot time
+			using hugepages= and not freed afterwards.
 
 	i8042.direct	[HW] Put keyboard port into non-translated mode
 	i8042.dumbkbd	[HW] Pretend that controller can only read data from