mm: compaction: early termination in compact_nodes()

No need to continue try compact memory if pending fatal signal, allow loop
termination earlier in compact_nodes().

The existing fatal_signal_pending() check does make compact_zone()
break out of the while loop, but it still enters the next zone/next
nid, and some unnecessary functions(eg, lru_add_drain) are called. 
There was no observable benefit from the new test, it is just found
from code inspection when refactoring compact_node().

Link: https://lkml.kernel.org/r/20240208022508.1771534-1-wangkefeng.wang@huawei.comSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/compaction.c

@@ -2808,7 +2808,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
  * reaching score targets due to various back-off conditions, such as,
  * contention on per-node or per-zone locks.
  */
-static void compact_node(pg_data_t *pgdat, bool proactive)
+static int compact_node(pg_data_t *pgdat, bool proactive)
 {
 	int zoneid;
 	struct zone *zone;
@@ -2826,6 +2826,9 @@ static void compact_node(pg_data_t *pgdat, bool proactive)
 		if (!populated_zone(zone))
 			continue;
 
+		if (fatal_signal_pending(current))
+			return -EINTR;
+
 		cc.zone = zone;
 
 		compact_zone(&cc, NULL);
@@ -2837,18 +2840,25 @@ static void compact_node(pg_data_t *pgdat, bool proactive)
 					     cc.total_free_scanned);
 		}
 	}
+
+	return 0;
 }
 
 /* Compact all zones of all nodes in the system */
-static void compact_nodes(void)
+static int compact_nodes(void)
 {
-	int nid;
+	int ret, nid;
 
 	/* Flush pending updates to the LRU lists */
 	lru_add_drain_all();
 
-	for_each_online_node(nid)
-		compact_node(NODE_DATA(nid), false);
+	for_each_online_node(nid) {
+		ret = compact_node(NODE_DATA(nid), false);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 
 static int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
@@ -2894,9 +2904,9 @@ static int sysctl_compaction_handler(struct ctl_table *table, int write,
 		return -EINVAL;
 
 	if (write)
-		compact_nodes();
+		ret = compact_nodes();
 
-	return 0;
+	return ret;
 }
 
 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)