[PATCH 2/2] mm: Lock PGDAT_RECLAIM_LOCKED with acquire memory ordering

[Mathieu Desnoyers]

The PGDAT_RECLAIM_LOCKED bit is used to provide mutual exclusion of
node reclaim for struct pglist_data using a single bit.

Use test_and_set_bit_lock rather than test_and_set_bit to test-and-set
PGDAT_RECLAIM_LOCKED with an acquire memory ordering semantic.

This changes the "lock" acquisition from a full barrier to an acquire
memory ordering, which is weaker. The acquire semi-permeable barrier
paired with the release on unlock is sufficient for this mutual
exclusion use-case.

No behavior change intended other than to reduce overhead by using
the appropriate barrier.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Parri <parri.andrea@xxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Jade Alglave <j.alglave@xxxxxxxxx>
Cc: Luc Maranget <luc.maranget@xxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d7e27d5c24e7..021b25bdba91 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7567,7 +7567,7 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
 	if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
 		return NODE_RECLAIM_NOSCAN;
 
-	if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
+	if (test_and_set_bit_lock(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
 		return NODE_RECLAIM_NOSCAN;
 
 	ret = __node_reclaim(pgdat, gfp_mask, order);
-- 
2.25.1