mm/memory_hotplug: update comment regarding zone shuffling

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.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Acked-by: Michal Hocko <mhocko@suse.com>
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>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Scott Cheloha <cheloha@linux.ibm.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Link: https://lkml.kernel.org/r/20201005121534.15649-6-david@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index d397af3..6f20357 100644 (file)
--- 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);