+++ /dev/null
-From: Peter Zijlstra <a.p.zijlstra@chello.nl>
-Subject: mm: add support for non block device backed swap files
-Patch-mainline: No
-References: FATE#303834
-
-New addres_space_operations methods are added:
- 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 *);
-
-When during sys_swapon() the ->swapon() method is found and returns no error
-the swapper_space.a_ops will proxy to sis->swap_file->f_mapping->a_ops, and
-make use of ->swap_{out,in}() to write/read swapcache pages.
-
-The ->swapon() method will be used to communicate to the file that the VM
-relies on it, and the address_space should take adequate measures (like
-reserving memory for mempools or the like). The ->swapoff() method will be
-called on sys_swapoff() when ->swapon() was found and returned no error.
-
-This new interface can be used to obviate the need for ->bmap in the swapfile
-code. A filesystem would need to load (and maybe even allocate) the full block
-map for a file into memory and pin it there on ->swapon() so that
-->swap_{out,in}() have instant access to it. It can be released on ->swapoff().
-
-The reason to provide ->swap_{out,in}() over using {write,read}page() is to
- 1) make a distinction between swapcache and pagecache pages, and
- 2) to provide a struct file * for credential context (normally not needed
- in the context of writepage, as the page content is normally dirtied
- using either of the following interfaces:
- write_{begin,end}()
- {prepare,commit}_write()
- page_mkwrite()
- which do have the file context.
-
-[miklos@szeredi.hu: cleanups]
-Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
-Acked-by: Neil Brown <neilb@suse.de>
-Acked-by: Suresh Jayaraman <sjayaraman@suse.de>
-
----
- Documentation/filesystems/Locking | 22 ++++++++++++++++
- Documentation/filesystems/vfs.txt | 18 +++++++++++++
- include/linux/buffer_head.h | 2 -
- include/linux/fs.h | 9 ++++++
- include/linux/swap.h | 4 ++
- mm/page_io.c | 52 ++++++++++++++++++++++++++++++++++++++
- mm/swap_state.c | 4 +-
- mm/swapfile.c | 32 +++++++++++++++++++++--
- 8 files changed, 137 insertions(+), 6 deletions(-)
-
---- a/Documentation/filesystems/Locking
-+++ b/Documentation/filesystems/Locking
-@@ -169,6 +169,10 @@ 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
-@@ -190,6 +194,10 @@ 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
-
- ->prepare_write(), ->commit_write(), ->sync_page() and ->readpage()
- may be called from the request handler (/dev/loop).
-@@ -289,6 +297,20 @@ 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)
---- a/Documentation/filesystems/vfs.txt
-+++ b/Documentation/filesystems/vfs.txt
-@@ -539,6 +539,11 @@ 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.
-@@ -724,6 +729,19 @@ 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
- ===============
-
---- a/include/linux/buffer_head.h
-+++ b/include/linux/buffer_head.h
-@@ -345,7 +345,7 @@ static inline void invalidate_inode_buff
- 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 invalidate_bdev(struct block_device *bdev) {}
--
-+static inline void block_sync_page(struct page *) { }
-
- #endif /* CONFIG_BLOCK */
- #endif /* _LINUX_BUFFER_HEAD_H */
---- a/include/linux/fs.h
-+++ b/include/linux/fs.h
-@@ -525,6 +525,15 @@ 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);
- };
-
- /*
---- a/include/linux/swap.h
-+++ b/include/linux/swap.h
-@@ -120,6 +120,7 @@ enum {
- SWP_USED = (1 << 0), /* is slot in swap_info[] used? */
- SWP_WRITEOK = (1 << 1), /* ok to write to this swap? */
- SWP_ACTIVE = (SWP_USED | SWP_WRITEOK),
-+ SWP_FILE = (1 << 2), /* file swap area */
- /* add others here before... */
- SWP_SCANNING = (1 << 8), /* refcount in scan_swap_map */
- };
-@@ -217,6 +218,8 @@ extern void swap_unplug_io_fn(struct bac
- /* linux/mm/page_io.c */
- extern int swap_readpage(struct file *, 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 */
-@@ -249,6 +252,7 @@ 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 can_share_swap_page(struct page *);
- extern int remove_exclusive_swap_page(struct page *);
- struct backing_dev_info;
---- a/mm/page_io.c
-+++ b/mm/page_io.c
-@@ -17,6 +17,7 @@
- #include <linux/bio.h>
- #include <linux/swapops.h>
- #include <linux/writeback.h>
-+#include <linux/buffer_head.h>
- #include <trace/swap.h>
- #include <asm/pgtable.h>
-
-@@ -98,11 +99,23 @@ 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 (remove_exclusive_swap_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->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) {
-@@ -122,13 +135,52 @@ 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 file *file, struct page *page)
- {
- struct bio *bio;
- int ret = 0;
-+ struct swap_info_struct *sis = page_swap_info(page);
-
- BUG_ON(!PageLocked(page));
- 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) {
---- a/mm/swapfile.c
-+++ b/mm/swapfile.c
-@@ -1018,6 +1018,14 @@ 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);
-+ }
- }
-
- /*
-@@ -1092,7 +1100,9 @@ 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;
-@@ -1103,13 +1113,22 @@ 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;
-
-@@ -1683,7 +1702,7 @@ SYSCALL_DEFINE2(swapon, const char __use
- else
- p->prio = --least_priority;
- p->swap_map = swap_map;
-- p->flags = SWP_ACTIVE;
-+ p->flags |= SWP_WRITEOK;
- nr_swap_pages += nr_good_pages;
- total_swap_pages += nr_good_pages;
-
-@@ -1823,6 +1842,13 @@ 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.
---- a/mm/swap_state.c
-+++ b/mm/swap_state.c
-@@ -27,8 +27,8 @@
- */
- 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,
- };
-
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