mm, compaction: check if a page has been captured before draining PCP pages

If a page has been captured then draining is unnecssary so check first for
a captured page.

Link: https://lkml.kernel.org/r/20230125134434.18017-3-mgorman@techsingularity.netSigned-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Chuyi Zhou <zhouchuyi@bytedance.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/compaction.c

@@ -2439,6 +2439,12 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 			}
 		}
 
+		/* Stop if a page has been captured */
+		if (capc && capc->page) {
+			ret = COMPACT_SUCCESS;
+			break;
+		}
+
 check_drain:
 		/*
 		 * Has the migration scanner moved away from the previous
@@ -2457,12 +2463,6 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 				last_migrated_pfn = 0;
 			}
 		}
-
-		/* Stop if a page has been captured */
-		if (capc && capc->page) {
-			ret = COMPACT_SUCCESS;
-			break;
-		}
 	}
 
 out: