Commit 93146d98 authored Aug 06, 2020 by David Hildenbrand Committed by Linus Torvalds Aug 07, 2020

mm/memory_hotplug: document why shuffle_zone() is relevant



It's not completely obvious why we have to shuffle the complete zone -
introduced in commit e900a918 ("mm: shuffle initial free memory to
improve memory-side-cache utilization") - because some sort of shuffling
is already performed when onlining pages via __free_one_page(), placing
MAX_ORDER-1 pages either to the head or the tail of the freelist.  Let's
document why we have to shuffle the complete zone when exposing larger,
contiguous physical memory areas to the buddy.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Link: http://lkml.kernel.org/r/20200624094741.9918-3-david@redhat.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 56b9413b

mm/memory_hotplug.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -831,6 +831,14 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
		zone->zone_pgdat->node_present_pages += onlined_pages;
		pgdat_resize_unlock(zone->zone_pgdat, &flags);

		/*
		* 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.
		*/
		shuffle_zone(zone);

		node_states_set_node(nid, &arg);

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