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arc: update comment about HIGHMEM implementation

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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>
This commit is contained in:
Mike Rapoport
2021-06-28 19:42:43 -07:00
committed by Linus Torvalds
parent fdb7d9b7ac
commit e7793e5390
1 changed files with 5 additions and 8 deletions
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13
arch/arc/mm/init.c
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@ -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);