arc: update comment about HIGHMEM implementation

Arc does not use DISCONTIGMEM to implement high memory, update the comment
describing how high memory works to reflect this.

Link: https://lkml.kernel.org/r/20210608091316.3622-3-rppt@kernel.org
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
index e2ed355..397a201 100644 (file)
--- a/arch/arc/mm/init.c
+++ b/arch/arc/mm/init.c
@@ -139,16 +139,13 @@ void __init setup_arch_memory(void)
 
 #ifdef CONFIG_HIGHMEM
        /*
-        * Populate a new node with highmem
-        *
         * On ARC (w/o PAE) HIGHMEM addresses are actually smaller (0 based)
-        * than addresses in normal ala low memory (0x8000_0000 based).
+        * than addresses in normal aka low memory (0x8000_0000 based).
         * Even with PAE, the huge peripheral space hole would waste a lot of
-        * mem with single mem_map[]. This warrants a mem_map per region design.
-        * Thus HIGHMEM on ARC is imlemented with DISCONTIGMEM.
-        *
-        * DISCONTIGMEM in turns requires multiple nodes. node 0 above is
-        * populated with normal memory zone while node 1 only has highmem
+        * mem with single contiguous mem_map[].
+        * Thus when HIGHMEM on ARC is enabled the memory map corresponding
+        * to the hole is freed and ARC specific version of pfn_valid()
+        * handles the hole in the memory map.
         */
 #ifdef CONFIG_DISCONTIGMEM
        node_set_online(1);