tmpfs: move swap swizzling into shmem

move_to_swap_cache and move_from_swap_cache functions (which swizzle a page
between tmpfs page cache and swap cache, to avoid page copying) are only used
by shmem.c; and our subsequent fix for unionfs needs different treatments in
the two instances of move_from_swap_cache.  Move them from swap_state.c into
their callsites shmem_writepage, shmem_unuse_inode and shmem_getpage, making
add_to_swap_cache externally visible.

shmem.c likes to say set_page_dirty where swap_state.c liked to say
SetPageDirty: respect that diversity, which __set_page_dirty_no_writeback
makes moot (and implies we should lose that "shift page from clean_pages to
dirty_pages list" comment: it's on neither).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 34 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
index c75eda2c9cc5..65b81c92738f 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -67,8 +67,7 @@ void show_swap_cache_info(void)
  * add_to_swap_cache resembles add_to_page_cache on swapper_space,
  * but sets SwapCache flag and private instead of mapping and index.
  */
-static int add_to_swap_cache(struct page *page, swp_entry_t entry,
-                               gfp_t gfp_mask)
+int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 {
         int error;
 
@@ -183,38 +182,6 @@ void delete_from_swap_cache(struct page *page)
         page_cache_release(page);
 }
 
-/*
- * Strange swizzling function only for use by shmem_writepage
- */
-int move_to_swap_cache(struct page *page, swp_entry_t entry)
-{
-        int err = add_to_swap_cache(page, entry, GFP_ATOMIC);
-        if (!err) {
-                remove_from_page_cache(page);
-                page_cache_release(page);       /* pagecache ref */
-                if (!swap_duplicate(entry))
-                        BUG();
-                SetPageDirty(page);
-        }
-        return err;
-}
-
-/*
- * Strange swizzling function for shmem_getpage (and shmem_unuse)
- */
-int move_from_swap_cache(struct page *page, unsigned long index,
-                struct address_space *mapping)
-{
-        int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
-        if (!err) {
-                delete_from_swap_cache(page);
-                /* shift page from clean_pages to dirty_pages list */
-                ClearPageDirty(page);
-                set_page_dirty(page);
-        }
-        return err;
-}
-
 /* 
  * If we are the only user, then try to free up the swap cache. 
  *