[PATCH v3 1/3] mm: replace migrate_prep with lru_add_drain_all

[Minchan Kim <minchan@kernel.org>]

Currently, migrate_prep is merely a wrapper of lru_cache_add_all.
There is not much to gain from having additional abstraction.

Use lru_add_drain_all instead of migrate_prep, which would be more
descriptive.

note: migrate_prep_local in compaction.c changed into lru_add_drain
to avoid CPU schedule cost with involving many other CPUs to keep
keep old behavior.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 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, 11 insertions(+), 32 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 3a389633b68f..6155d97ec76c 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -45,8 +45,6 @@ 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,
@@ -66,9 +64,6 @@ 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 e04f4476e68e..3be017ececc0 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2319,7 +2319,8 @@ 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);
 
-	migrate_prep_local();
+	/* lru_add_drain_all could be expensive with involving other CPUs */
+	lru_add_drain();
 
 	while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
 		int err;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index ab51132547b8..fc024e97be37 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1124,7 +1124,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 	int err = 0;
 	nodemask_t tmp;
 
-	migrate_prep();
+	lru_add_drain_all();
 
 	mmap_read_lock(mm);
 
@@ -1323,7 +1323,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 
 	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
 
-		migrate_prep();
+		lru_add_drain_all();
 	}
 	{
 		NODEMASK_SCRATCH(scratch);
diff --git a/mm/migrate.c b/mm/migrate.c
index 62b81d5257aa..45f925e10f5a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -57,28 +57,6 @@
 
 #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;
@@ -1769,7 +1747,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 	int start, i;
 	int err = 0, err1;
 
-	migrate_prep();
+	lru_add_drain_all();
 
 	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 2e8348936df8..f05a8db741ca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8467,7 +8467,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 		.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
 	};
 
-	migrate_prep();
+	lru_add_drain_all();
 
 	while (pfn < end || !list_empty(&cc->migratepages)) {
 		if (fatal_signal_pending(current)) {
diff --git a/mm/swap.c b/mm/swap.c
index 31b844d4ed94..441d1ae1f285 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -729,6 +729,11 @@ 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.
-- 
2.30.1.766.gb4fecdf3b7-goog