From d3c1bf42afb07db55dfd705310e1850354fb8d2b Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@google.com>
Date: Fri, 19 Mar 2021 12:34:42 -0700
Subject: [PATCH] Revert "FROMLIST: mm: replace migrate_prep with
 lru_add_drain_all"

This reverts commit 134ac2d4dcfec0c0487d57e4b78efbef8714b883.

Bug: 180018981
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: I579c72398447f770c235e4fefd246f1dbbd250d0
---
 include/linux/migrate.h |  5 +++++
 mm/compaction.c         |  3 +--
 mm/mempolicy.c          |  4 ++--
 mm/migrate.c            | 24 +++++++++++++++++++++++-
 mm/page_alloc.c         |  2 +-
 mm/swap.c               |  5 -----
 6 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 8512469ff6fb..63b4d114b415 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -45,6 +45,8 @@ extern struct page *alloc_migration_target(struct page *page, unsigned long priv
 extern int isolate_movable_page(struct page *page, isolate_mode_t mode);
 extern void putback_movable_page(struct page *page);
 
+extern void migrate_prep(void);
+extern void migrate_prep_local(void);
 extern void migrate_page_states(struct page *newpage, struct page *page);
 extern void migrate_page_copy(struct page *newpage, struct page *page);
 extern int migrate_huge_page_move_mapping(struct address_space *mapping,
@@ -64,6 +66,9 @@ static inline struct page *alloc_migration_target(struct page *page,
 static inline int isolate_movable_page(struct page *page, isolate_mode_t mode)
 	{ return -EBUSY; }
 
+static inline int migrate_prep(void) { return -ENOSYS; }
+static inline int migrate_prep_local(void) { return -ENOSYS; }
+
 static inline void migrate_page_states(struct page *newpage, struct page *page)
 {
 }
diff --git a/mm/compaction.c b/mm/compaction.c
index 34d99d7d1a6a..dba424447473 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2275,8 +2275,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 	trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
 				cc->free_pfn, end_pfn, sync);
 
-	/* lru_add_drain_all could be expensive with involving other CPUs */
-	lru_add_drain();
+	migrate_prep_local();
 
 	while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
 		int err;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index dcb86c9d27ae..a4a6b030305e 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1127,7 +1127,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 	int err = 0;
 	nodemask_t tmp;
 
-	lru_add_drain_all();
+	migrate_prep();
 
 	mmap_read_lock(mm);
 
@@ -1326,7 +1326,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 
 	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
 
-		lru_add_drain_all();
+		migrate_prep();
 	}
 	{
 		NODEMASK_SCRATCH(scratch);
diff --git a/mm/migrate.c b/mm/migrate.c
index d41cea28ee76..fd4cde426c80 100644
--- a/mm/migrate.c
+++ b/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;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e97edd589408..e02ac9014537 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8520,7 +8520,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 	if (cc->alloc_contig && cc->mode == MIGRATE_ASYNC)
 		max_tries = 1;
 
-	lru_add_drain_all();
+	migrate_prep();
 
 	while (pfn < end || !list_empty(&cc->migratepages)) {
 		if (fatal_signal_pending(current)) {
diff --git a/mm/swap.c b/mm/swap.c
index 6f8cc8462fab..d160a07830a7 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -753,11 +753,6 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
 }
 
 /*
- * lru_add_drain_all() usually needs to be called before we start compiling
- * a list of pages to be migrated using isolate_lru_page(). 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.
- *
  * Doesn't need any cpu hotplug locking because we do rely on per-cpu
  * kworkers being shut down before our page_alloc_cpu_dead callback is
  * executed on the offlined cpu.