Re: [PATCH v1 5/5] mm/memory_hotplug: update comment regarding zone shuffling

[Wei Yang]

On Mon, Sep 28, 2020 at 08:21:10PM +0200, David Hildenbrand wrote:
>As we no longer shuffle via generic_online_page() and when undoing
>isolation, we can simplify the comment.
>
>We now effectively shuffle only once (properly) when onlining new
>memory.
>
>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
>Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
>Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
>Cc: Vlastimil Babka <vbabka@xxxxxxx>
>Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
>Cc: Oscar Salvador <osalvador@xxxxxxx>
>Cc: Mike Rapoport <rppt@xxxxxxxxxx>
>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>

>---
> mm/memory_hotplug.c | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index 9db80ee29caa..c589bd8801bb 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -859,13 +859,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
> 	undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
> 
> 	/*
>-	 * When exposing larger, physically contiguous memory areas to the
>-	 * buddy, shuffling in the buddy (when freeing onlined pages, putting
>-	 * them either to the head or the tail of the freelist) is only helpful
>-	 * for maintaining the shuffle, but not for creating the initial
>-	 * shuffle. Shuffle the whole zone to make sure the just onlined pages
>-	 * are properly distributed across the whole freelist. Make sure to
>-	 * shuffle once pageblocks are no longer isolated.
>+	 * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
>+	 * the tail of the freelist when undoing isolation). Shuffle the whole
>+	 * zone to make sure the just onlined pages are properly distributed
>+	 * across the whole freelist - to create an initial shuffle.
> 	 */
> 	shuffle_zone(zone);
> 
>-- 
>2.26.2

-- 
Wei Yang
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