7 files changed, 105 insertions, 3 deletions

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index e0cce2a5f820..2db1900d7538 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -206,6 +206,8 @@ prototypes:
         int (*launder_page)(struct page *);
         int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
         int (*error_remove_page)(struct address_space *, struct page *);
+        int (*swap_activate)(struct file *);
+        int (*swap_deactivate)(struct file *);
 
 locking rules:
         All except set_page_dirty and freepage may block
@@ -229,6 +231,8 @@ migratepage:		yes (both)
 launder_page:           yes
 is_partially_uptodate:  yes
 error_remove_page:      yes
+swap_activate:          no
+swap_deactivate:        no
 
         ->write_begin(), ->write_end(), ->sync_page() and ->readpage()
 may be called from the request handler (/dev/loop).
@@ -330,6 +334,15 @@ cleaned, or an error value if not. Note that in order to prevent the page
 getting mapped back in and redirtied, it needs to be kept locked
 across the entire operation.
 
+        ->swap_activate will be called with a non-zero argument on
+files backing (non block device backed) swapfiles. A return value
+of zero indicates success, in which case this file can be used for
+backing swapspace. The swapspace operations will be proxied to the
+address space operations.
+
+        ->swap_deactivate() will be called in the sys_swapoff()
+path after ->swap_activate() returned success.
+
 ----------------------- file_lock_operations ------------------------------
 prototypes:
         void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index aa754e01464e..065aa2dc0835 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -592,6 +592,8 @@ struct address_space_operations {
         int (*migratepage) (struct page *, struct page *);
         int (*launder_page) (struct page *);
         int (*error_remove_page) (struct mapping *mapping, struct page *page);
+        int (*swap_activate)(struct file *);
+        int (*swap_deactivate)(struct file *);
 };
 
   writepage: called by the VM to write a dirty page to backing store.
@@ -760,6 +762,16 @@ struct address_space_operations {
         Setting this implies you deal with pages going away under you,
         unless you have them locked or reference counts increased.
 
+  swap_activate: Called when swapon is used on a file to allocate
+        space if necessary and pin the block lookup information in
+        memory. A return value of zero indicates success,
+        in which case this file can be used to back swapspace. The
+        swapspace operations will be proxied to this address space's
+        ->swap_{out,in} methods.
+
+  swap_deactivate: Called during swapoff on files where swap_activate
+        was successful.
+
 
 The File Object
 ===============
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9d77309da153..38356ab827c9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -638,6 +638,10 @@ struct address_space_operations {
         int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
                                         unsigned long);
         int (*error_remove_page)(struct address_space *, struct page *);
+
+        /* swapfile support */
+        int (*swap_activate)(struct file *file);
+        int (*swap_deactivate)(struct file *file);
 };
 
 extern const struct address_space_operations empty_aops;
diff --git a/include/linux/swap.h b/include/linux/swap.h
index e62425ded2ed..ab230b1ebf61 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -151,6 +151,7 @@ enum {
         SWP_SOLIDSTATE  = (1 << 4),     /* blkdev seeks are cheap */
         SWP_CONTINUED   = (1 << 5),     /* swap_map has count continuation */
         SWP_BLKDEV      = (1 << 6),     /* its a block device */
+        SWP_FILE        = (1 << 7),     /* set after swap_activate success */
                                         /* add others here before... */
         SWP_SCANNING    = (1 << 8),     /* refcount in scan_swap_map */
 };
@@ -320,6 +321,7 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
 /* linux/mm/page_io.c */
 extern int swap_readpage(struct page *);
 extern int swap_writepage(struct page *page, struct writeback_control *wbc);
+extern int swap_set_page_dirty(struct page *page);
 extern void end_swap_bio_read(struct bio *bio, int err);
 
 /* linux/mm/swap_state.c */
diff --git a/mm/page_io.c b/mm/page_io.c
index 34f02923744c..307a3e795290 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -17,6 +17,7 @@
 #include <linux/swap.h>
 #include <linux/bio.h>
 #include <linux/swapops.h>
+#include <linux/buffer_head.h>
 #include <linux/writeback.h>
 #include <linux/frontswap.h>
 #include <asm/pgtable.h>
@@ -94,6 +95,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 {
         struct bio *bio;
         int ret = 0, rw = WRITE;
+        struct swap_info_struct *sis = page_swap_info(page);
 
         if (try_to_free_swap(page)) {
                 unlock_page(page);
@@ -105,6 +107,32 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
                 end_page_writeback(page);
                 goto out;
         }
+
+        if (sis->flags & SWP_FILE) {
+                struct kiocb kiocb;
+                struct file *swap_file = sis->swap_file;
+                struct address_space *mapping = swap_file->f_mapping;
+                struct iovec iov = {
+                        .iov_base = page_address(page),
+                        .iov_len  = PAGE_SIZE,
+                };
+
+                init_sync_kiocb(&kiocb, swap_file);
+                kiocb.ki_pos = page_file_offset(page);
+                kiocb.ki_left = PAGE_SIZE;
+                kiocb.ki_nbytes = PAGE_SIZE;
+
+                unlock_page(page);
+                ret = mapping->a_ops->direct_IO(KERNEL_WRITE,
+                                                &kiocb, &iov,
+                                                kiocb.ki_pos, 1);
+                if (ret == PAGE_SIZE) {
+                        count_vm_event(PSWPOUT);
+                        ret = 0;
+                }
+                return ret;
+        }
+
         bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
         if (bio == NULL) {
                 set_page_dirty(page);
@@ -126,6 +154,7 @@ int swap_readpage(struct page *page)
 {
         struct bio *bio;
         int ret = 0;
+        struct swap_info_struct *sis = page_swap_info(page);
 
         VM_BUG_ON(!PageLocked(page));
         VM_BUG_ON(PageUptodate(page));
@@ -134,6 +163,17 @@ int swap_readpage(struct page *page)
                 unlock_page(page);
                 goto out;
         }
+
+        if (sis->flags & SWP_FILE) {
+                struct file *swap_file = sis->swap_file;
+                struct address_space *mapping = swap_file->f_mapping;
+
+                ret = mapping->a_ops->readpage(swap_file, page);
+                if (!ret)
+                        count_vm_event(PSWPIN);
+                return ret;
+        }
+
         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
         if (bio == NULL) {
                 unlock_page(page);
@@ -145,3 +185,15 @@ int swap_readpage(struct page *page)
 out:
         return ret;
 }
+
+int swap_set_page_dirty(struct page *page)
+{
+        struct swap_info_struct *sis = page_swap_info(page);
+
+        if (sis->flags & SWP_FILE) {
+                struct address_space *mapping = sis->swap_file->f_mapping;
+                return mapping->a_ops->set_page_dirty(page);
+        } else {
+                return __set_page_dirty_no_writeback(page);
+        }
+}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index c85b5590cccd..0cb36fb1f61c 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -27,7 +27,7 @@
  */
 static const struct address_space_operations swap_aops = {
         .writepage      = swap_writepage,
-        .set_page_dirty = __set_page_dirty_no_writeback,
+        .set_page_dirty = swap_set_page_dirty,
         .migratepage    = migrate_page,
 };
 
diff --git a/mm/swapfile.c b/mm/swapfile.c
index f89af5ba2eb2..6ffc87602f4a 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1329,6 +1329,14 @@ static void destroy_swap_extents(struct swap_info_struct *sis)
                 list_del(&se->list);
                 kfree(se);
         }
+
+        if (sis->flags & SWP_FILE) {
+                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);
+        }
 }
 
 /*
@@ -1410,7 +1418,9 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
  */
 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 {
-        struct inode *inode;
+        struct file *swap_file = sis->swap_file;
+        struct address_space *mapping = swap_file->f_mapping;
+        struct inode *inode = mapping->host;
         unsigned blocks_per_page;
         unsigned long page_no;
         unsigned blkbits;
@@ -1421,13 +1431,22 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
         int nr_extents = 0;
         int ret;
 
-        inode = sis->swap_file->f_mapping->host;
         if (S_ISBLK(inode->i_mode)) {
                 ret = add_swap_extent(sis, 0, sis->max, 0);
                 *span = sis->pages;
                 goto out;
         }
 
+        if (mapping->a_ops->swap_activate) {
+                ret = mapping->a_ops->swap_activate(swap_file);
+                if (!ret) {
+                        sis->flags |= SWP_FILE;
+                        ret = add_swap_extent(sis, 0, sis->max, 0);
+                        *span = sis->pages;
+                }
+                goto out;
+        }
+
         blkbits = inode->i_blkbits;
         blocks_per_page = PAGE_SIZE >> blkbits;