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 --- 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(-) Index: linux-2.6/include/linux/swap.h =================================================================== --- linux-2.6.orig/include/linux/swap.h +++ linux-2.6/include/linux/swap.h @@ -121,6 +121,7 @@ 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 */ }; @@ -274,6 +275,8 @@ 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 */ @@ -306,6 +309,7 @@ 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 *); extern int remove_exclusive_swap_page_ref(struct page *); Index: linux-2.6/mm/page_io.c =================================================================== --- linux-2.6.orig/mm/page_io.c +++ linux-2.6/mm/page_io.c @@ -17,6 +17,7 @@ #include #include #include +#include #include 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 (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) { @@ -120,13 +133,52 @@ 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) { Index: linux-2.6/mm/swap_state.c =================================================================== --- linux-2.6.orig/mm/swap_state.c +++ linux-2.6/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, }; Index: linux-2.6/mm/swapfile.c =================================================================== --- linux-2.6.orig/mm/swapfile.c +++ linux-2.6/mm/swapfile.c @@ -1031,6 +1031,14 @@ 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); + } } /* @@ -1105,7 +1113,9 @@ 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; @@ -1116,13 +1126,22 @@ 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; @@ -1691,7 +1710,7 @@ asmlinkage long sys_swapon(const char __ mutex_lock(&swapon_mutex); spin_lock(&swap_lock); - p->flags = SWP_ACTIVE; + p->flags |= SWP_WRITEOK; nr_swap_pages += nr_good_pages; total_swap_pages += nr_good_pages; @@ -1816,6 +1835,13 @@ 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. Index: linux-2.6/include/linux/fs.h =================================================================== --- linux-2.6.orig/include/linux/fs.h +++ linux-2.6/include/linux/fs.h @@ -509,6 +509,15 @@ 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); }; /* Index: linux-2.6/Documentation/filesystems/Locking =================================================================== --- linux-2.6.orig/Documentation/filesystems/Locking +++ linux-2.6/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) Index: linux-2.6/include/linux/buffer_head.h =================================================================== --- linux-2.6.orig/include/linux/buffer_head.h +++ linux-2.6/include/linux/buffer_head.h @@ -336,7 +336,7 @@ 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 */ Index: linux-2.6/Documentation/filesystems/vfs.txt =================================================================== --- linux-2.6.orig/Documentation/filesystems/vfs.txt +++ linux-2.6/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 =============== -- -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html