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

[Michal Hocko <mhocko@xxxxxxxx>]

On Mon 28-09-20 20:21:10, 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>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  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

-- 
Michal Hocko
SUSE Labs