mm: lock PGDAT_RECLAIM_LOCKED with acquire memory ordering

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.

Link: https://lkml.kernel.org/r/20250312141014.129725-2-mathieu.desnoyers@efficios.com
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index bbd3913e38879caab4c0d42dc51a57af8d4d8ebc..2bc740637a6c2ff8f3579ee5c302e6f6701ac8b6 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7577,7 +7577,7 @@ 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);