mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS

The SWP_FILE flag serves two purposes: to make swap_{read,write}page() go
through the filesystem, and to make swapoff() call ->swap_deactivate().
For Btrfs, we want the latter but not the former, so split this flag into
two.  This makes us always call ->swap_deactivate() if ->swap_activate()
succeeded, not just if it didn't add any swap extents itself.

This also resolves the issue of the very misleading name of SWP_FILE,
which is only used for swap files over NFS.

Link: http://lkml.kernel.org/r/6d63d8668c4287a4f6d203d65696e96f80abdfc7.1536704650.git.osandov@fb.com
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2681e50592c5..f0c7e4c11bab 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1003,7 +1003,7 @@ start_over:
                         goto nextsi;
                 }
                 if (size == SWAPFILE_CLUSTER) {
-                        if (!(si->flags & SWP_FILE))
+                        if (!(si->flags & SWP_FS))
                                 n_ret = swap_alloc_cluster(si, swp_entries);
                 } else
                         n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
@@ -2299,12 +2299,13 @@ static void destroy_swap_extents(struct swap_info_struct *sis)
                 kfree(se);
         }
 
-        if (sis->flags & SWP_FILE) {
+        if (sis->flags & SWP_ACTIVATED) {
                 struct file *swap_file = sis->swap_file;
                 struct address_space *mapping = swap_file->f_mapping;
 
-                sis->flags &= ~SWP_FILE;
-                mapping->a_ops->swap_deactivate(swap_file);
+                sis->flags &= ~SWP_ACTIVATED;
+                if (mapping->a_ops->swap_deactivate)
+                        mapping->a_ops->swap_deactivate(swap_file);
         }
 }
 
@@ -2400,8 +2401,10 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 
         if (mapping->a_ops->swap_activate) {
                 ret = mapping->a_ops->swap_activate(sis, swap_file, span);
+                if (ret >= 0)
+                        sis->flags |= SWP_ACTIVATED;
                 if (!ret) {
-                        sis->flags |= SWP_FILE;
+                        sis->flags |= SWP_FS;
                         ret = add_swap_extent(sis, 0, sis->max, 0);
                         *span = sis->pages;
                 }