/* * fs/mpage.c * * Copyright (C) 2002, Linus Torvalds. * * Contains functions related to preparing and submitting BIOs which contain * multiple pagecache pages. * * 15May2002 akpm@zip.com.au * Initial version */ #include <linux/kernel.h> #include <linux/module.h> #include <linux/bio.h> #include <linux/fs.h> #include <linux/buffer_head.h> #include <linux/blkdev.h> #include <linux/highmem.h> #include <linux/prefetch.h> #include <linux/mpage.h> #include <linux/pagevec.h> /* * The largest-sized BIO which this code will assemble, in bytes. Set this * to PAGE_CACHE_SIZE if your drivers are broken. */ #define MPAGE_BIO_MAX_SIZE BIO_MAX_SIZE /* * I/O completion handler for multipage BIOs. * * The mpage code never puts partial pages into a BIO (except for end-of-file). * If a page does not map to a contiguous run of blocks then it simply falls * back to block_read_full_page(). * * Why is this? If a page's completion depends on a number of different BIOs * which can complete in any order (or at the same time) then determining the * status of that page is hard. See end_buffer_async_read() for the details. * There is no point in duplicating all that complexity. */ static void mpage_end_io_read(struct bio *bio) { const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1; do { struct page *page = bvec->bv_page; if (--bvec >= bio->bi_io_vec) prefetchw(&bvec->bv_page->flags); if (uptodate) { SetPageUptodate(page); } else { ClearPageUptodate(page); SetPageError(page); } unlock_page(page); } while (bvec >= bio->bi_io_vec); bio_put(bio); } static void mpage_end_io_write(struct bio *bio) { const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1; do { struct page *page = bvec->bv_page; if (--bvec >= bio->bi_io_vec) prefetchw(&bvec->bv_page->flags); if (!uptodate) SetPageError(page); end_page_writeback(page); } while (bvec >= bio->bi_io_vec); bio_put(bio); } struct bio *mpage_bio_submit(int rw, struct bio *bio) { bio->bi_vcnt = bio->bi_idx; bio->bi_idx = 0; bio->bi_end_io = mpage_end_io_read; if (rw == WRITE) bio->bi_end_io = mpage_end_io_write; submit_bio(rw, bio); return NULL; } static struct bio * mpage_alloc(struct block_device *bdev, sector_t first_sector, int nr_vecs, int gfp_flags) { struct bio *bio; bio = bio_alloc(gfp_flags, nr_vecs); if (bio == NULL && (current->flags & PF_MEMALLOC)) { while (!bio && (nr_vecs /= 2)) bio = bio_alloc(gfp_flags, nr_vecs); } if (bio) { bio->bi_bdev = bdev; bio->bi_vcnt = nr_vecs; bio->bi_idx = 0; bio->bi_size = 0; bio->bi_sector = first_sector; bio->bi_io_vec[0].bv_page = NULL; } return bio; } /** * mpage_readpages - populate an address space with some pages, and * start reads against them. * * @mapping: the address_space * @pages: The address of a list_head which contains the target pages. These * pages have their ->index populated and are otherwise uninitialised. * * The page at @pages->prev has the lowest file offset, and reads should be * issued in @pages->prev to @pages->next order. * * @nr_pages: The number of pages at *@pages * @get_block: The filesystem's block mapper function. * * This function walks the pages and the blocks within each page, building and * emitting large BIOs. * * If anything unusual happens, such as: * * - encountering a page which has buffers * - encountering a page which has a non-hole after a hole * - encountering a page with non-contiguous blocks * * then this code just gives up and calls the buffer_head-based read function. * It does handle a page which has holes at the end - that is a common case: * the end-of-file on blocksize < PAGE_CACHE_SIZE setups. * * BH_Boundary explanation: * * There is a problem. The mpage read code assembles several pages, gets all * their disk mappings, and then submits them all. That's fine, but obtaining * the disk mappings may require I/O. Reads of indirect blocks, for example. * * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be * submitted in the following order: * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16 * because the indirect block has to be read to get the mappings of blocks * 13,14,15,16. Obviously, this impacts performance. * * So what we do it to allow the filesystem's get_block() function to set * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block * after this one will require I/O against a block which is probably close to * this one. So you should push what I/O you have currently accumulated. * * This all causes the disk requests to be issued in the correct order. */ static struct bio * do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages, sector_t *last_block_in_bio, get_block_t get_block) { struct inode *inode = page->mapping->host; const unsigned blkbits = inode->i_blkbits; const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits; const unsigned blocksize = 1 << blkbits; struct bio_vec *bvec; sector_t block_in_file; sector_t last_block; sector_t blocks[MAX_BUF_PER_PAGE]; unsigned page_block; unsigned first_hole = blocks_per_page; struct block_device *bdev = NULL; struct buffer_head bh; if (page_has_buffers(page)) goto confused; block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits); last_block = (inode->i_size + blocksize - 1) >> blkbits; for (page_block = 0; page_block < blocks_per_page; page_block++, block_in_file++) { bh.b_state = 0; if (block_in_file < last_block) { if (get_block(inode, block_in_file, &bh, 0)) goto confused; } if (!buffer_mapped(&bh)) { if (first_hole == blocks_per_page) first_hole = page_block; continue; } if (first_hole != blocks_per_page) goto confused; /* hole -> non-hole */ /* Contiguous blocks? */ if (page_block && blocks[page_block-1] != bh.b_blocknr-1) goto confused; blocks[page_block] = bh.b_blocknr; bdev = bh.b_bdev; } if (first_hole != blocks_per_page) { memset(kmap(page) + (first_hole << blkbits), 0, PAGE_CACHE_SIZE - (first_hole << blkbits)); flush_dcache_page(page); kunmap(page); if (first_hole == 0) { SetPageUptodate(page); unlock_page(page); goto out; } } /* * This page will go to BIO. Do we need to send this BIO off first? */ if (bio && (bio->bi_idx == bio->bi_vcnt || *last_block_in_bio != blocks[0] - 1)) bio = mpage_bio_submit(READ, bio); if (bio == NULL) { unsigned nr_bvecs = MPAGE_BIO_MAX_SIZE / PAGE_CACHE_SIZE; if (nr_bvecs > nr_pages) nr_bvecs = nr_pages; bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), nr_bvecs, GFP_KERNEL); if (bio == NULL) goto confused; } bvec = &bio->bi_io_vec[bio->bi_idx++]; bvec->bv_page = page; bvec->bv_len = (first_hole << blkbits); bvec->bv_offset = 0; bio->bi_size += bvec->bv_len; if (buffer_boundary(&bh) || (first_hole != blocks_per_page)) bio = mpage_bio_submit(READ, bio); else *last_block_in_bio = blocks[blocks_per_page - 1]; out: return bio; confused: if (bio) bio = mpage_bio_submit(READ, bio); block_read_full_page(page, get_block); goto out; } int mpage_readpages(struct address_space *mapping, struct list_head *pages, unsigned nr_pages, get_block_t get_block) { struct bio *bio = NULL; unsigned page_idx; sector_t last_block_in_bio = 0; struct pagevec lru_pvec; pagevec_init(&lru_pvec); for (page_idx = 0; page_idx < nr_pages; page_idx++) { struct page *page = list_entry(pages->prev, struct page, list); prefetchw(&page->flags); list_del(&page->list); if (!add_to_page_cache(page, mapping, page->index)) { bio = do_mpage_readpage(bio, page, nr_pages - page_idx, &last_block_in_bio, get_block); if (!pagevec_add(&lru_pvec, page)) __pagevec_lru_add(&lru_pvec); } else { page_cache_release(page); } } pagevec_lru_add(&lru_pvec); BUG_ON(!list_empty(pages)); if (bio) mpage_bio_submit(READ, bio); return 0; } EXPORT_SYMBOL(mpage_readpages); /* * This isn't called much at all */ int mpage_readpage(struct page *page, get_block_t get_block) { struct bio *bio = NULL; sector_t last_block_in_bio = 0; bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio, get_block); if (bio) mpage_bio_submit(READ, bio); return 0; } EXPORT_SYMBOL(mpage_readpage); /* * Writing is not so simple. * * If the page has buffers then they will be used for obtaining the disk * mapping. We only support pages which are fully mapped-and-dirty, with a * special case for pages which are unmapped at the end: end-of-file. * * If the page has no buffers (preferred) then the page is mapped here. * * If all blocks are found to be contiguous then the page can go into the * BIO. Otherwise fall back to the mapping's writepage(). * * FIXME: This code wants an estimate of how many pages are still to be * written, so it can intelligently allocate a suitably-sized BIO. For now, * just allocate full-size (16-page) BIOs. */ static inline struct bio * mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block, sector_t *last_block_in_bio, int *ret) { struct inode *inode = page->mapping->host; const unsigned blkbits = inode->i_blkbits; unsigned long end_index; const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits; struct bio_vec *bvec; sector_t last_block; sector_t block_in_file; sector_t blocks[MAX_BUF_PER_PAGE]; unsigned page_block; unsigned first_unmapped = blocks_per_page; struct block_device *bdev = NULL; int boundary = 0; if (page_has_buffers(page)) { struct buffer_head *head = page_buffers(page); struct buffer_head *bh = head; /* If they're all mapped and dirty, do it */ page_block = 0; do { BUG_ON(buffer_locked(bh)); if (!buffer_mapped(bh)) { /* * unmapped dirty buffers are created by * __set_page_dirty_buffers -> mmapped data */ if (buffer_dirty(bh)) goto confused; if (first_unmapped == blocks_per_page) first_unmapped = page_block; continue; } if (first_unmapped != blocks_per_page) goto confused; /* hole -> non-hole */ if (!buffer_dirty(bh) || !buffer_uptodate(bh)) goto confused; if (page_block) { if (bh->b_blocknr != blocks[page_block-1] + 1) goto confused; } blocks[page_block++] = bh->b_blocknr; boundary = buffer_boundary(bh); bdev = bh->b_bdev; } while ((bh = bh->b_this_page) != head); if (first_unmapped) goto page_is_mapped; /* * Page has buffers, but they are all unmapped. The page was * created by pagein or read over a hole which was handled by * block_read_full_page(). If this address_space is also * using mpage_readpages then this can rarely happen. */ goto confused; } /* * The page has no buffers: map it to disk */ BUG_ON(!PageUptodate(page)); block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits); last_block = (inode->i_size - 1) >> blkbits; for (page_block = 0; page_block < blocks_per_page; ) { struct buffer_head map_bh; map_bh.b_state = 0; if (get_block(inode, block_in_file, &map_bh, 1)) goto confused; if (buffer_new(&map_bh)) unmap_underlying_metadata(map_bh.b_bdev, map_bh.b_blocknr); if (page_block) { if (map_bh.b_blocknr != blocks[page_block-1] + 1) goto confused; } blocks[page_block++] = map_bh.b_blocknr; boundary = buffer_boundary(&map_bh); bdev = map_bh.b_bdev; if (block_in_file == last_block) break; block_in_file++; } if (page_block == 0) buffer_error(); first_unmapped = page_block; end_index = inode->i_size >> PAGE_CACHE_SHIFT; if (page->index >= end_index) { unsigned offset = inode->i_size & (PAGE_CACHE_SIZE - 1); if (page->index > end_index || !offset) goto confused; memset(kmap(page) + offset, 0, PAGE_CACHE_SIZE - offset); flush_dcache_page(page); kunmap(page); } page_is_mapped: /* * This page will go to BIO. Do we need to send this BIO off first? */ if (bio && (bio->bi_idx == bio->bi_vcnt || *last_block_in_bio != blocks[0] - 1)) bio = mpage_bio_submit(WRITE, bio); if (bio == NULL) { unsigned nr_bvecs = MPAGE_BIO_MAX_SIZE / PAGE_CACHE_SIZE; bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), nr_bvecs, GFP_NOFS|__GFP_HIGH); if (bio == NULL) goto confused; } /* * OK, we have our BIO, so we can now mark the buffers clean. Make * sure to only clean buffers which we know we'll be writing. */ if (page_has_buffers(page)) { struct buffer_head *head = page_buffers(page); struct buffer_head *bh = head; unsigned buffer_counter = 0; do { if (buffer_counter++ == first_unmapped) break; clear_buffer_dirty(bh); bh = bh->b_this_page; } while (bh != head); } bvec = &bio->bi_io_vec[bio->bi_idx++]; bvec->bv_page = page; bvec->bv_len = (first_unmapped << blkbits); bvec->bv_offset = 0; bio->bi_size += bvec->bv_len; BUG_ON(PageWriteback(page)); SetPageWriteback(page); unlock_page(page); if (boundary || (first_unmapped != blocks_per_page)) bio = mpage_bio_submit(WRITE, bio); else *last_block_in_bio = blocks[blocks_per_page - 1]; goto out; confused: if (bio) bio = mpage_bio_submit(WRITE, bio); *ret = page->mapping->a_ops->writepage(page); out: return bio; } /** * mpage_writepages - walk the list of dirty pages of the given * address space and writepage() all of them. * * @mapping: address space structure to write * @nr_to_write: subtract the number of written pages from *@nr_to_write * @get_block: the filesystem's block mapper function. * If this is NULL then use a_ops->writepage. Otherwise, go * direct-to-BIO. * * This is a library function, which implements the writepages() * address_space_operation. * * (The next two paragraphs refer to code which isn't here yet, but they * explain the presence of address_space.io_pages) * * Pages can be moved from clean_pages or locked_pages onto dirty_pages * at any time - it's not possible to lock against that. So pages which * have already been added to a BIO may magically reappear on the dirty_pages * list. And generic_writepages() will again try to lock those pages. * But I/O has not yet been started against the page. Thus deadlock. * * To avoid this, the entire contents of the dirty_pages list are moved * onto io_pages up-front. We then walk io_pages, locking the * pages and submitting them for I/O, moving them to locked_pages. * * This has the added benefit of preventing a livelock which would otherwise * occur if pages are being dirtied faster than we can write them out. * * If a page is already under I/O, generic_writepages() skips it, even * if it's dirty. This is desirable behaviour for memory-cleaning writeback, * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() * and msync() need to guarentee that all the data which was dirty at the time * the call was made get new I/O started against them. The way to do this is * to run filemap_fdatawait() before calling filemap_fdatawrite(). * * It's fairly rare for PageWriteback pages to be on ->dirty_pages. It * means that someone redirtied the page while it was under I/O. */ int mpage_writepages(struct address_space *mapping, int *nr_to_write, get_block_t get_block) { struct bio *bio = NULL; sector_t last_block_in_bio = 0; int ret = 0; int done = 0; struct pagevec pvec; int (*writepage)(struct page *); writepage = NULL; if (get_block == NULL) writepage = mapping->a_ops->writepage; pagevec_init(&pvec); write_lock(&mapping->page_lock); list_splice_init(&mapping->dirty_pages, &mapping->io_pages); while (!list_empty(&mapping->io_pages) && !done) { struct page *page = list_entry(mapping->io_pages.prev, struct page, list); list_del(&page->list); if (PageWriteback(page)) { if (PageDirty(page)) { list_add(&page->list, &mapping->dirty_pages); continue; } list_add(&page->list, &mapping->locked_pages); continue; } if (!PageDirty(page)) { list_add(&page->list, &mapping->clean_pages); continue; } list_add(&page->list, &mapping->locked_pages); page_cache_get(page); write_unlock(&mapping->page_lock); lock_page(page); if (page->mapping && !PageWriteback(page) && TestClearPageDirty(page)) { if (writepage) { ret = (*writepage)(page); } else { bio = mpage_writepage(bio, page, get_block, &last_block_in_bio, &ret); } if ((current->flags & PF_MEMALLOC) && !PageActive(page) && PageLRU(page)) { if (!pagevec_add(&pvec, page)) pagevec_deactivate_inactive(&pvec); page = NULL; } if (ret || (nr_to_write && --(*nr_to_write) <= 0)) done = 1; } else { unlock_page(page); } if (page) page_cache_release(page); write_lock(&mapping->page_lock); } /* * Put the rest back, in the correct order. */ list_splice_init(&mapping->io_pages, mapping->dirty_pages.prev); write_unlock(&mapping->page_lock); pagevec_deactivate_inactive(&pvec); if (bio) mpage_bio_submit(WRITE, bio); return ret; } EXPORT_SYMBOL(mpage_writepages);