Revert "FROMLIST: mm: replace migrate_prep with lru_add_drain_all"

This reverts commit 134ac2d4dc.

Bug: 180018981
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: I579c72398447f770c235e4fefd246f1dbbd250d0

mm/migrate.c

@@ -57,6 +57,28 @@
 
 #include "internal.h"
 
+/*
+ * migrate_prep() needs to be called before we start compiling a list of pages
+ * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
+ * undesirable, use migrate_prep_local()
+ */
+void migrate_prep(void)
+{
+	/*
+	 * Clear the LRU lists so pages can be isolated.
+	 * Note that pages may be moved off the LRU after we have
+	 * drained them. Those pages will fail to migrate like other
+	 * pages that may be busy.
+	 */
+	lru_add_drain_all();
+}
+
+/* Do the necessary work of migrate_prep but not if it involves other CPUs */
+void migrate_prep_local(void)
+{
+	lru_add_drain();
+}
+
 int isolate_movable_page(struct page *page, isolate_mode_t mode)
 {
 	struct address_space *mapping;
@@ -1697,7 +1719,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 	int start, i;
 	int err = 0, err1;
 
-	lru_add_drain_all();
+	migrate_prep();
 
 	for (i = start = 0; i < nr_pages; i++) {
 		const void __user *p;