===================================================================
@@ -174,6 +174,10 @@ prototypes:
int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
loff_t offset, unsigned long nr_segs);
int (*launder_page) (struct page *);
+ int (*swapon) (struct file *);
+ int (*swapoff) (struct file *);
+ int (*swap_out) (struct file *, struct page *, struct writeback_control *);
+ int (*swap_in) (struct file *, struct page *);
locking rules:
All except set_page_dirty may block
@@ -193,6 +197,10 @@ invalidatepage: no yes
releasepage: no yes
direct_IO: no
launder_page: no yes
+swapon no
+swapoff no
+swap_out no yes, unlocks
+swap_in no yes, unlocks
->write_begin(), ->write_end(), ->sync_page() and ->readpage()
may be called from the request handler (/dev/loop).
@@ -292,6 +300,20 @@ cleaned, or an error value if not. Note
getting mapped back in and redirtied, it needs to be kept locked
across the entire operation.
+ ->swapon() 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.
+
+ ->swapoff() will be called in the sys_swapoff() path when ->swapon()
+returned success.
+
+ ->swap_out() when swapon() returned success, this method is used to
+write the swap page.
+
+ ->swap_in() when swapon() returned success, this method is used to
+read the swap page.
+
Note: currently almost all instances of address_space methods are
using BKL for internal serialization and that's one of the worst sources
of contention. Normally they are calling library functions (in fs/buffer.c)
===================================================================
@@ -536,6 +536,11 @@ struct address_space_operations {
/* migrate the contents of a page to the specified target */
int (*migratepage) (struct page *, struct page *);
int (*launder_page) (struct page *);
+ int (*swapon)(struct file *);
+ int (*swapoff)(struct file *);
+ int (*swap_out)(struct file *file, struct page *page,
+ struct writeback_control *wbc);
+ int (*swap_in)(struct file *file, struct page *page);
};
writepage: called by the VM to write a dirty page to backing store.
@@ -694,6 +699,19 @@ struct address_space_operations {
prevent redirtying the page, it is kept locked during the whole
operation.
+ swapon: Called when swapon is used on a file. 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.
+
+ swapoff: Called during swapoff on files where swapon was successfull.
+
+ swap_out: Called to write a swapcache page to a backing store, similar to
+ writepage.
+
+ swap_in: Called to read a swapcache page from a backing store, similar to
+ readpage.
+
The File Object
===============
===================================================================
@@ -339,6 +339,7 @@ static inline int inode_has_buffers(stru
static inline void invalidate_inode_buffers(struct inode *inode) {}
static inline int remove_inode_buffers(struct inode *inode) { return 1; }
static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }
+static inline void block_sync_page(struct page *) { }
#endif /* CONFIG_BLOCK */
#endif /* _LINUX_BUFFER_HEAD_H */
===================================================================
@@ -595,6 +595,15 @@ struct address_space_operations {
int (*launder_page) (struct page *);
int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
unsigned long);
+
+ /*
+ * swapfile support
+ */
+ int (*swapon)(struct file *file);
+ int (*swapoff)(struct file *file);
+ int (*swap_out)(struct file *file, struct page *page,
+ struct writeback_control *wbc);
+ int (*swap_in)(struct file *file, struct page *page);
};
/*
===================================================================
@@ -120,6 +120,7 @@ struct swap_extent {
enum {
SWP_USED = (1 << 0), /* is slot in swap_info[] used? */
SWP_WRITEOK = (1 << 1), /* ok to write to this swap? */
+ SWP_FILE = (1 << 2), /* file swap area */
SWP_DISCARDABLE = (1 << 2), /* blkdev supports discard */
SWP_DISCARDING = (1 << 3), /* now discarding a free cluster */
SWP_SOLIDSTATE = (1 << 4), /* blkdev seeks are cheap */
@@ -258,6 +259,8 @@ extern void swap_unplug_io_fn(struct bac
/* linux/mm/page_io.c */
extern int swap_readpage(struct page *);
extern int swap_writepage(struct page *page, struct writeback_control *wbc);
+extern void swap_sync_page(struct page *page);
+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 */
@@ -293,6 +296,7 @@ extern unsigned int count_swap_pages(int
extern sector_t map_swap_page(struct swap_info_struct *, pgoff_t);
extern sector_t swapdev_block(int, pgoff_t);
extern struct swap_info_struct *get_swap_info_struct(unsigned);
+extern struct swap_info_struct *page_swap_info(struct page *);
extern int reuse_swap_page(struct page *);
extern int try_to_free_swap(struct page *);
struct backing_dev_info;
===================================================================
@@ -17,6 +17,7 @@
#include <linux/bio.h>
#include <linux/swapops.h>
#include <linux/writeback.h>
+#include <linux/buffer_head.h>
#include <asm/pgtable.h>
static struct bio *get_swap_bio(gfp_t gfp_flags, pgoff_t index,
@@ -97,11 +98,23 @@ int swap_writepage(struct page *page, st
{
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);
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->swap_out(swap_file, page, wbc);
+ if (!ret)
+ count_vm_event(PSWPOUT);
+ return ret;
+ }
+
bio = get_swap_bio(GFP_NOIO, page_private(page), page,
end_swap_bio_write);
if (bio == NULL) {
@@ -120,13 +133,51 @@ out:
return ret;
}
+void swap_sync_page(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;
+
+ if (mapping->a_ops->sync_page)
+ mapping->a_ops->sync_page(page);
+ } else {
+ block_sync_page(page);
+ }
+}
+
+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_nobuffers(page);
+ }
+}
+
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));
+
+ if (sis->flags & SWP_FILE) {
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+
+ ret = mapping->a_ops->swap_in(swap_file, page);
+ if (!ret)
+ count_vm_event(PSWPIN);
+ return ret;
+ }
bio = get_swap_bio(GFP_KERNEL, page_private(page), page,
end_swap_bio_read);
if (bio == NULL) {
===================================================================
@@ -28,8 +28,8 @@
*/
static const struct address_space_operations swap_aops = {
.writepage = swap_writepage,
- .sync_page = block_sync_page,
- .set_page_dirty = __set_page_dirty_nobuffers,
+ .sync_page = swap_sync_page,
+ .set_page_dirty = swap_set_page_dirty,
.migratepage = migrate_page,
};
===================================================================
@@ -1335,6 +1335,14 @@ static void destroy_swap_extents(struct
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->swapoff(swap_file);
+ }
}
/*
@@ -1409,7 +1417,9 @@ add_swap_extent(struct swap_info_struct
*/
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;
@@ -1420,13 +1430,22 @@ static int setup_swap_extents(struct swa
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 done;
}
+ if (mapping->a_ops->swapon) {
+ ret = mapping->a_ops->swapon(swap_file);
+ if (!ret) {
+ sis->flags |= SWP_FILE;
+ ret = add_swap_extent(sis, 0, sis->max, 0);
+ *span = sis->pages;
+ }
+ goto done;
+ }
+
blkbits = inode->i_blkbits;
blocks_per_page = PAGE_SIZE >> blkbits;
@@ -2163,6 +2182,13 @@ get_swap_info_struct(unsigned type)
return &swap_info[type];
}
+struct swap_info_struct *page_swap_info(struct page *page)
+{
+ swp_entry_t swap = { .val = page_private(page) };
+ BUG_ON(!PageSwapCache(page));
+ return &swap_info[swp_type(swap)];
+}
+
/*
* swap_lock prevents swap_map being freed. Don't grab an extra
* reference on the swaphandle, it doesn't matter if it becomes unused.