linux-kernel - [PATCH v2 2/9] arc: update comment about HIGHMEM implementation

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Message-Id: <20210604064916.26580-3-rppt@kernel.org>
Date:   Fri,  4 Jun 2021 09:49:09 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Jonathan Corbet <corbet@....net>,
        Matt Turner <mattst88@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Richard Henderson <rth@...ddle.net>,
        Vineet Gupta <vgupta@...opsys.com>, kexec@...ts.infradead.org,
        linux-alpha@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org, linux-xtensa@...ux-xtensa.org,
        linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org
Subject: [PATCH v2 2/9] arc: update comment about HIGHMEM implementation

From: Mike Rapoport <rppt@...ux.ibm.com>

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

Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
---
 arch/arc/mm/init.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
index e2ed355438c9..397a201adfe3 100644
--- 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);
-- 
2.28.0