linux-kernel - Re: [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling

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Date:   Tue, 20 Oct 2020 19:21:52 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-hyperv@...r.kernel.org,
        xen-devel@...ts.xenproject.org, linux-acpi@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Michal Hocko <mhocko@...e.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Rapoport <rppt@...nel.org>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>
Subject: Re: [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone
 shuffling

On 10/5/20 2:15 PM, 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.
> 
> Reviewed-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
> Acked-by: Michal Hocko <mhocko@...e.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>   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 03a00cb68bf7..b44d4c7ba73b 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -858,13 +858,10 @@ 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);
>   
>