On Thu, 2008-01-10 at 08:37 +0000, Christoph Hellwig wrote: > Peter, any chance you could chime in here? I have this patch to add swap_out/_in methods. I expect we can loosen the requirement for swapcache pages and change the name a little. previously posted here: http://lkml.org/lkml/2007/5/4/143 --- Subject: mm: add support for non block device backed swap files New addres_space_operations methods are added: int swapfile(struct address_space *, int); int swap_out(struct file *, struct page *, struct writeback_control *); int swap_in(struct file *, struct page *); When during sys_swapon() the swapfile() 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 swapfile method will be used to communicate to the address_space that the VM relies on it, and the address_space should take adequate measures (like reserving memory for mempools or the like). 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 ->swapfile(,1) so that ->swap_{out,in}() have instant access to it. It can be released on ->swapfile(,0). 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. Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> --- Documentation/filesystems/Locking | 19 ++++++++++++ Documentation/filesystems/vfs.txt | 17 +++++++++++ include/linux/buffer_head.h | 2 - include/linux/fs.h | 8 +++++ include/linux/swap.h | 3 + mm/Kconfig | 3 + mm/page_io.c | 58 ++++++++++++++++++++++++++++++++++++++ mm/swap_state.c | 5 +++ mm/swapfile.c | 22 +++++++++++++- 9 files changed, 135 insertions(+), 2 deletions(-) Index: linux-2.6/include/linux/swap.h =================================================================== --- linux-2.6.orig/include/linux/swap.h +++ linux-2.6/include/linux/swap.h @@ -164,6 +164,7 @@ 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 */ }; @@ -261,6 +262,8 @@ 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 */ 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 <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, @@ -102,6 +103,18 @@ int swap_writepage(struct page *page, st unlock_page(page); goto out; } +#ifdef CONFIG_SWAP_FILE + { + struct swap_info_struct *sis = page_swap_info(page); + if (sis->flags & SWP_FILE) { + ret = sis->swap_file->f_mapping-> + a_ops->swap_out(sis->swap_file, page, wbc); + if (!ret) + count_vm_event(PSWPOUT); + return ret; + } + } +#endif bio = get_swap_bio(GFP_NOIO, page_private(page), page, end_swap_bio_write); if (bio == NULL) { @@ -120,6 +133,39 @@ out: return ret; } +#ifdef CONFIG_SWAP_FILE +void swap_sync_page(struct page *page) +{ + struct swap_info_struct *sis = page_swap_info(page); + + if (sis->flags & SWP_FILE) { + const struct address_space_operations * a_ops = + sis->swap_file->f_mapping->a_ops; + if (a_ops->sync_page) + 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) { + const struct address_space_operations * a_ops = + sis->swap_file->f_mapping->a_ops; + int (*spd)(struct page *) = a_ops->set_page_dirty; +#ifdef CONFIG_BLOCK + if (!spd) + spd = __set_page_dirty_buffers; +#endif + return (*spd)(page); + } + + return __set_page_dirty_nobuffers(page); +} +#endif + int swap_readpage(struct file *file, struct page *page) { struct bio *bio; @@ -127,6 +173,18 @@ int swap_readpage(struct file *file, str BUG_ON(!PageLocked(page)); ClearPageUptodate(page); +#ifdef CONFIG_SWAP_FILE + { + struct swap_info_struct *sis = page_swap_info(page); + if (sis->flags & SWP_FILE) { + ret = sis->swap_file->f_mapping-> + a_ops->swap_in(sis->swap_file, page); + if (!ret) + count_vm_event(PSWPIN); + return ret; + } + } +#endif 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 +27,13 @@ */ static const struct address_space_operations swap_aops = { .writepage = swap_writepage, +#ifdef CONFIG_SWAP_FILE + .sync_page = swap_sync_page, + .set_page_dirty = swap_set_page_dirty, +#else .sync_page = block_sync_page, .set_page_dirty = __set_page_dirty_nobuffers, +#endif .migratepage = migrate_page, }; Index: linux-2.6/mm/swapfile.c =================================================================== --- linux-2.6.orig/mm/swapfile.c +++ linux-2.6/mm/swapfile.c @@ -1015,6 +1015,13 @@ static void destroy_swap_extents(struct list_del(&se->list); kfree(se); } +#ifdef CONFIG_SWAP_FILE + if (sis->flags & SWP_FILE) { + sis->flags &= ~SWP_FILE; + sis->swap_file->f_mapping->a_ops-> + swapfile(sis->swap_file->f_mapping, 0); + } +#endif } /* @@ -1107,6 +1114,19 @@ static int setup_swap_extents(struct swa goto done; } +#ifdef CONFIG_SWAP_FILE + if (sis->swap_file->f_mapping->a_ops->swapfile) { + ret = sis->swap_file->f_mapping->a_ops-> + swapfile(sis->swap_file->f_mapping, 1); + if (!ret) { + sis->flags |= SWP_FILE; + ret = add_swap_extent(sis, 0, sis->max, 0); + *span = sis->pages; + } + goto done; + } +#endif + blkbits = inode->i_blkbits; blocks_per_page = PAGE_SIZE >> blkbits; @@ -1671,7 +1691,7 @@ 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; Index: linux-2.6/include/linux/fs.h =================================================================== --- linux-2.6.orig/include/linux/fs.h +++ linux-2.6/include/linux/fs.h @@ -479,6 +479,14 @@ struct address_space_operations { int (*migratepage) (struct address_space *, struct page *, struct page *); int (*launder_page) (struct page *); + + /* + * swapfile support + */ + int (*swapfile)(struct address_space *, int); + 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 @@ -171,6 +171,9 @@ prototypes: int (*direct_IO)(int, struct kiocb *, const struct iovec *iov, loff_t offset, unsigned long nr_segs); int (*launder_page) (struct page *); + int (*swapfile) (struct address_space *, int); + 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 @@ -192,6 +195,9 @@ invalidatepage: no yes releasepage: no yes direct_IO: no launder_page: no yes +swapfile 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). @@ -291,6 +297,19 @@ cleaned, or an error value if not. Note getting mapped back in and redirtied, it needs to be kept locked across the entire operation. + ->swapfile() will be called with a non zero argument on address spaces +backing non block device backed swapfiles. A return value of zero indicates +success. In which case this address space can be used for backing swapspace. +The swapspace operations will be proxied to the address space operations. +Swapoff will call this method with a zero argument to release the address +space. + + ->swap_out() when swapfile() returned success, this method is used to +write the swap page. + + ->swap_in() when swapfile() 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/mm/Kconfig =================================================================== --- linux-2.6.orig/mm/Kconfig +++ linux-2.6/mm/Kconfig @@ -185,6 +185,9 @@ config BOUNCE def_bool y depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM) +config SWAP_FILE + def_bool n + config NR_QUICK int depends on QUICKLIST 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 @@ -335,7 +335,7 @@ 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 @@ -542,6 +542,10 @@ 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 (*swapfile)(struct address_space *, int); + 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. @@ -727,6 +731,19 @@ struct address_space_operations { prevent redirtying the page, it is kept locked during the whole operation. + swapfile: Called with a non-zero argument when swapon is used on a file. A + return value of zero indicates success. In which case this + address_space can be used to back swapspace. The swapspace operations + will be proxied to this address space's ->swap_{out,in} methods. + Swapoff will call this method with a zero argument to release the + address space. + + 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 linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
