mm: convert zone->managed_pages to atomic variable

totalram_pages, zone->managed_pages and totalhigh_pages updates are
protected by managed_page_count_lock, but readers never care about it.
Convert these variables to atomic to avoid readers potentially seeing a
store tear.

This patch converts zone->managed_pages.  Subsequent patches will convert
totalram_panges, totalhigh_pages and eventually managed_page_count_lock
will be removed.

Main motivation was that managed_page_count_lock handling was complicating
things.  It was discussed in length here,
https://lore.kernel.org/patchwork/patch/995739/#1181785 So it seemes
better to remove the lock and convert variables to atomic, with preventing
poteintial store-to-read tearing as a bonus.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arun KS <[email protected]>
Suggested-by: Michal Hocko <[email protected]>
Suggested-by: Vlastimil Babka <[email protected]>
Reviewed-by: Konstantin Khlebnikov <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Reviewed-by: Pavel Tatashin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/memblock.c b/mm/memblock.c
index 81ae63ca78d0..0068f87af1e8 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1950,7 +1950,7 @@ void reset_node_managed_pages(pg_data_t *pgdat)
 	struct zone *z;
 
 	for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
-		z->managed_pages = 0;
+		atomic_long_set(&z->managed_pages, 0);
 }
 
 void __init reset_all_zones_managed_pages(void)