FROMLIST: mm: replace migrate_[prep|finish] with lru_cache_[disable|enable]

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.

Bug: 180018981
Link: https://lore.kernel.org/linux-mm/20210319175127.886124-2-minchan@kernel.org/
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: I2f298c9ff53c8693527f1207ff25ab76a4ac3ada
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4283c08..58abb6d 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;
 
-	migrate_prep();
+	lru_cache_disable();
 
 	mmap_read_lock(mm);
 
@@ -1212,7 +1212,7 @@ 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;
@@ -1328,7 +1328,7 @@ 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);
@@ -1377,7 +1377,7 @@ 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;
 }