[181/192] arc: update comment about HIGHMEM implementation

Commit Message

Andrew Morton June 29, 2021, 2:42 a.m. UTC

From: Mike Rapoport <[e-mail]>
Subject: 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/[e-mail]
Signed-off-by: Mike Rapoport <[e-mail]>
Acked-by: Vineet Gupta <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: Ivan Kokshaysky <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Matt Turner <[e-mail]>
Cc: Richard Henderson <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 arch/arc/mm/init.c |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

Patch

--- a/arch/arc/mm/init.c~arc-update-comment-about-highmem-implementation
+++ a/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);