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>

2 files changed, 13 insertions, 38 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 7be94342bf06..e577adf4ae85 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -884,7 +884,9 @@ lost2:
 found:
         idx += offset;
         inode = &info->vfs_inode;
-        if (move_from_swap_cache(page, idx, inode->i_mapping) == 0) {
+        if (add_to_page_cache(page, inode->i_mapping, idx, GFP_ATOMIC) == 0) {
+                delete_from_swap_cache(page);
+                set_page_dirty(page);
                 info->flags |= SHMEM_PAGEIN;
                 shmem_swp_set(info, ptr + offset, 0);
         }
@@ -972,7 +974,8 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
         BUG_ON(!entry);
         BUG_ON(entry->val);
 
-        if (move_to_swap_cache(page, swap) == 0) {
+        if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
+                remove_from_page_cache(page);
                 shmem_swp_set(info, entry, swap.val);
                 shmem_swp_unmap(entry);
                 spin_unlock(&info->lock);
@@ -982,6 +985,9 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
                         list_move_tail(&info->swaplist, &shmem_swaplist);
                         spin_unlock(&shmem_swaplist_lock);
                 }
+                swap_duplicate(swap);
+                page_cache_release(page);       /* pagecache ref */
+                set_page_dirty(page);
                 unlock_page(page);
                 return 0;
         }
@@ -1217,13 +1223,15 @@ repeat:
                         SetPageUptodate(filepage);
                         set_page_dirty(filepage);
                         swap_free(swap);
-                } else if (!(error = move_from_swap_cache(
-                                swappage, idx, mapping))) {
+                } else if (!(error = add_to_page_cache(
+                                swappage, mapping, idx, GFP_ATOMIC))) {
                         info->flags |= SHMEM_PAGEIN;
                         shmem_swp_set(info, entry, 0);
                         shmem_swp_unmap(entry);
+                        delete_from_swap_cache(swappage);
                         spin_unlock(&info->lock);
                         filepage = swappage;
+                        set_page_dirty(filepage);
                         swap_free(swap);
                 } else {
                         shmem_swp_unmap(entry);
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. 
  *