[PATCH v4 2/3] mm: replace migrate_[prep|finish] with lru_cache_[disable|enable]

[Minchan Kim]

Currently, migrate_[prep|finish] is merely a wrapper of
lru_cache_[disable|enable]. There is not much to gain from
having additional abstraction.

Use lru_cache_[disable|enable] instead of migrate_[prep|finish],
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.

Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 include/linux/migrate.h |  7 -------
 mm/compaction.c         |  3 ++-
 mm/mempolicy.c          |  8 ++++----
 mm/migrate.c            | 28 ++--------------------------
 mm/page_alloc.c         |  4 ++--
 5 files changed, 10 insertions(+), 40 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 9e4a2dc8622c..6155d97ec76c 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -45,9 +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_finish(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,
@@ -67,10 +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_finish(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 495b43a4b0f8..6daf9cc4c843 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_cache_disable();
 
 	mmap_read_lock(mm);
 
@@ -1209,7 +1209,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 	}
 	mmap_read_unlock(mm);
 
-	migrate_finish();
+	lru_cache_enable();
 	if (err < 0)
 		return err;
 	return busy;
@@ -1325,7 +1325,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 
 	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
 
-		migrate_prep();
+		lru_cache_disable();
 	}
 	{
 		NODEMASK_SCRATCH(scratch);
@@ -1374,7 +1374,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 mpol_out:
 	mpol_put(new);
 	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
-		migrate_finish();
+		lru_cache_enable();
 	return err;
 }
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 4d6c306d41c6..acc9913e4303 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -57,30 +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.
-	 */
-	lru_cache_disable();
-}
-
-void migrate_finish(void)
-{
-	lru_cache_enable();
-}
-
-/* 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;
@@ -1771,7 +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_cache_disable();
 
 	for (i = start = 0; i < nr_pages; i++) {
 		const void __user *p;
@@ -1840,7 +1816,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 	if (err >= 0)
 		err = err1;
 out:
-	migrate_finish();
+	lru_cache_enable();
 	return err;
 }
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index af5d4eeb2999..bf1606c7965a 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_cache_disable();
 
 	while (pfn < end || !list_empty(&cc->migratepages)) {
 		if (fatal_signal_pending(current)) {
@@ -8496,7 +8496,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 				NULL, (unsigned long)&mtc, cc->mode, MR_CONTIG_RANGE);
 	}
 
-	migrate_finish();
+	lru_cache_enable();
 	if (ret < 0) {
 		putback_movable_pages(&cc->migratepages);
 		return ret;
-- 
2.31.0.rc2.261.g7f71774620-goog