mm/vmscan: simplify shrink_node()

The difference between sc->nr_reclaimed and nr_reclaimed is computed three
times.  Introduce a new variable to record the value, so it only needs to
be computed once.

Link: https://lkml.kernel.org/r/20230411061757.12041-1-haifeng.xu@shopee.comSigned-off-by: Haifeng Xu <haifeng.xu@shopee.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -6463,7 +6463,7 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 {
 	struct reclaim_state *reclaim_state = current->reclaim_state;
-	unsigned long nr_reclaimed, nr_scanned;
+	unsigned long nr_reclaimed, nr_scanned, nr_node_reclaimed;
 	struct lruvec *target_lruvec;
 	bool reclaimable = false;
 
@@ -6489,13 +6489,14 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 		reclaim_state->reclaimed_slab = 0;
 	}
 
+	nr_node_reclaimed = sc->nr_reclaimed - nr_reclaimed;
+
 	/* Record the subtree's reclaim efficiency */
 	if (!sc->proactive)
 		vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
-			   sc->nr_scanned - nr_scanned,
-			   sc->nr_reclaimed - nr_reclaimed);
+			   sc->nr_scanned - nr_scanned, nr_node_reclaimed);
 
-	if (sc->nr_reclaimed - nr_reclaimed)
+	if (nr_node_reclaimed)
 		reclaimable = true;
 
 	if (current_is_kswapd()) {
@@ -6557,8 +6558,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 	    test_bit(LRUVEC_CONGESTED, &target_lruvec->flags))
 		reclaim_throttle(pgdat, VMSCAN_THROTTLE_CONGESTED);
 
-	if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
-				    sc))
+	if (should_continue_reclaim(pgdat, nr_node_reclaimed, sc))
 		goto again;
 
 	/*