+ arc-update-comment-about-highmem-implementation.patch added to -mm tree

+ arc-update-comment-about-highmem-implementation.patch added to -mm tree

[akpm]

The patch titled
     Subject: arc: update comment about HIGHMEM implementation
has been added to the -mm tree.  Its filename is
     arc-update-comment-about-highmem-implementation.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/arc-update-comment-about-highmem-implementation.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/arc-update-comment-about-highmem-implementation.patch

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------------------------------------------------------
From: Mike Rapoport <rppt@linux.ibm.com>
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/20210608091316.3622-3-rppt@kernel.org
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
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>
---

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

--- 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);
_

Patches currently in -mm which might be from rppt@linux.ibm.com are

mm-mmzoneh-simplify-is_highmem_idx.patch
alpha-remove-discontigmem-and-numa.patch
arc-update-comment-about-highmem-implementation.patch
arc-remove-support-for-discontigmem.patch
m68k-remove-support-for-discontigmem.patch
mm-remove-config_discontigmem.patch
arch-mm-remove-stale-mentions-of-disconigmem.patch
docs-remove-description-of-discontigmem.patch
mm-replace-config_need_multiple_nodes-with-config_numa.patch
mm-replace-config_flat_node_mem_map-with-config_flatmem.patch
docs-procrst-meminfo-briefly-describe-gaps-in-memory-accounting.patch
include-linux-mmzoneh-add-documentation-for-pfn_valid.patch
memblock-update-initialization-of-reserved-pages.patch
arm64-decouple-check-whether-pfn-is-in-linear-map-from-pfn_valid.patch
arm64-drop-pfn_valid_within-and-simplify-pfn_valid.patch
mmap-make-mlock_future_check-global.patch
riscv-kconfig-make-direct-map-manipulation-options-depend-on-mmu.patch
set_memory-allow-querying-whether-set_direct_map_-is-actually-enabled.patch
mm-introduce-memfd_secret-system-call-to-create-secret-memory-areas.patch
pm-hibernate-disable-when-there-are-active-secretmem-users.patch
arch-mm-wire-up-memfd_secret-system-call-where-relevant.patch
secretmem-test-add-basic-selftest-for-memfd_secret2.patch