mm/migration: make isolate_movable_page() return int type

Patch series "HWPOISON: soft offlining for non-lru movable page", v6.

After Minchan's commit bda807d444 ("mm: migrate: support non-lru
movable page migration"), some type of non-lru page like zsmalloc and
virtio-balloon page also support migration.

Therefore, we can:

1) soft offlining no-lru movable pages, which means when memory
   corrected errors occur on a non-lru movable page, we can stop to use
   it by migrating data onto another page and disable the original
   (maybe half-broken) one.

2) enable memory hotplug for non-lru movable pages, i.e. we may offline
   blocks, which include such pages, by using non-lru page migration.

This patchset is heavily dependent on non-lru movable page migration.

This patch (of 4):

Change the return type of isolate_movable_page() from bool to int.  It
will return 0 when isolate movable page successfully, and return -EBUSY
when it isolates failed.

There is no functional change within this patch but prepare for later
patch.

[[email protected]: v6]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yisheng Xie <[email protected]>
Suggested-by: Michal Hocko <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Hanjun Guo <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Reza Arbab <[email protected]>
Cc: Taku Izumi <[email protected]>
Cc: Vitaly Kuznetsov <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xishi Qiu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/migrate.c

@@ -74,7 +74,7 @@ int migrate_prep_local(void)
 	return 0;
 }
 
-bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+int isolate_movable_page(struct page *page, isolate_mode_t mode)
 {
 	struct address_space *mapping;
 
@@ -125,14 +125,14 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 	__SetPageIsolated(page);
 	unlock_page(page);
 
-	return true;
+	return 0;
 
 out_no_isolated:
 	unlock_page(page);
 out_putpage:
 	put_page(page);
 out:
-	return false;
+	return -EBUSY;
 }
 
 /* It should be called on page which is PG_movable */