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@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.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 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

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@linux-foundation.org>
>Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>Cc: Mel Gorman <mgorman@techsingularity.net>
>Cc: Michal Hocko <mhocko@kernel.org>
>Cc: Dave Hansen <dave.hansen@intel.com>
>Cc: Vlastimil Babka <vbabka@suse.cz>
>Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
>Cc: Oscar Salvador <osalvador@suse.de>
>Cc: Mike Rapoport <rppt@kernel.org>
>Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.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 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
Help you, Help me

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@linux-foundation.org>
> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@kernel.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Michal Hocko <mhocko@suse.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 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