diff options
Diffstat (limited to 'fs/mpage.c')
| -rw-r--r-- | fs/mpage.c | 772 |
1 files changed, 772 insertions, 0 deletions
diff --git a/fs/mpage.c b/fs/mpage.c new file mode 100644 index 00000000000..e7d8d1a7760 --- /dev/null +++ b/fs/mpage.c @@ -0,0 +1,772 @@ +/* + * 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 + * 27Jun2002 axboe@suse.de + * use bio_add_page() to build bio's just the right size + */ + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/mm.h> +#include <linux/kdev_t.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/writeback.h> +#include <linux/backing-dev.h> +#include <linux/pagevec.h> + +/* + * 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 int mpage_end_io_read(struct bio *bio, unsigned int bytes_done, int err) +{ + const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); + struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1; + + if (bio->bi_size) + return 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); + return 0; +} + +static int mpage_end_io_write(struct bio *bio, unsigned int bytes_done, int err) +{ + const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); + struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1; + + if (bio->bi_size) + return 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); + return 0; +} + +struct bio *mpage_bio_submit(int rw, struct bio *bio) +{ + 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, + unsigned int __nocast 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_sector = first_sector; + } + return bio; +} + +/* + * support function for mpage_readpages. The fs supplied get_block might + * return an up to date buffer. This is used to map that buffer into + * the page, which allows readpage to avoid triggering a duplicate call + * to get_block. + * + * The idea is to avoid adding buffers to pages that don't already have + * them. So when the buffer is up to date and the page size == block size, + * this marks the page up to date instead of adding new buffers. + */ +static void +map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) +{ + struct inode *inode = page->mapping->host; + struct buffer_head *page_bh, *head; + int block = 0; + + if (!page_has_buffers(page)) { + /* + * don't make any buffers if there is only one buffer on + * the page and the page just needs to be set up to date + */ + if (inode->i_blkbits == PAGE_CACHE_SHIFT && + buffer_uptodate(bh)) { + SetPageUptodate(page); + return; + } + create_empty_buffers(page, 1 << inode->i_blkbits, 0); + } + head = page_buffers(page); + page_bh = head; + do { + if (block == page_block) { + page_bh->b_state = bh->b_state; + page_bh->b_bdev = bh->b_bdev; + page_bh->b_blocknr = bh->b_blocknr; + break; + } + page_bh = page_bh->b_this_page; + block++; + } while (page_bh != head); +} + +/** + * 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; + 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; + int length; + int fully_mapped = 1; + + if (page_has_buffers(page)) + goto confused; + + block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits); + last_block = (i_size_read(inode) + blocksize - 1) >> blkbits; + + bh.b_page = page; + 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)) { + fully_mapped = 0; + if (first_hole == blocks_per_page) + first_hole = page_block; + continue; + } + + /* some filesystems will copy data into the page during + * the get_block call, in which case we don't want to + * read it again. map_buffer_to_page copies the data + * we just collected from get_block into the page's buffers + * so readpage doesn't have to repeat the get_block call + */ + if (buffer_uptodate(&bh)) { + map_buffer_to_page(page, &bh, page_block); + goto confused; + } + + 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) { + char *kaddr = kmap_atomic(page, KM_USER0); + memset(kaddr + (first_hole << blkbits), 0, + PAGE_CACHE_SIZE - (first_hole << blkbits)); + flush_dcache_page(page); + kunmap_atomic(kaddr, KM_USER0); + if (first_hole == 0) { + SetPageUptodate(page); + unlock_page(page); + goto out; + } + } else if (fully_mapped) { + SetPageMappedToDisk(page); + } + + /* + * This page will go to BIO. Do we need to send this BIO off first? + */ + if (bio && (*last_block_in_bio != blocks[0] - 1)) + bio = mpage_bio_submit(READ, bio); + +alloc_new: + if (bio == NULL) { + bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), + min_t(int, nr_pages, bio_get_nr_vecs(bdev)), + GFP_KERNEL); + if (bio == NULL) + goto confused; + } + + length = first_hole << blkbits; + if (bio_add_page(bio, page, length, 0) < length) { + bio = mpage_bio_submit(READ, bio); + goto alloc_new; + } + + 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); + if (!PageUptodate(page)) + block_read_full_page(page, get_block); + else + unlock_page(page); + 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, 0); + for (page_idx = 0; page_idx < nr_pages; page_idx++) { + struct page *page = list_entry(pages->prev, struct page, lru); + + prefetchw(&page->flags); + list_del(&page->lru); + if (!add_to_page_cache(page, mapping, + page->index, GFP_KERNEL)) { + 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 struct bio * +__mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block, + sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc, + writepage_t writepage_fn) +{ + struct address_space *mapping = page->mapping; + 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; + 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; + sector_t boundary_block = 0; + struct block_device *boundary_bdev = NULL; + int length; + struct buffer_head map_bh; + loff_t i_size = i_size_read(inode); + + 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); + if (boundary) { + boundary_block = bh->b_blocknr; + boundary_bdev = bh->b_bdev; + } + 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 = (i_size - 1) >> blkbits; + map_bh.b_page = page; + for (page_block = 0; page_block < blocks_per_page; ) { + + 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 (buffer_boundary(&map_bh)) { + boundary_block = map_bh.b_blocknr; + boundary_bdev = map_bh.b_bdev; + } + 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++; + } + BUG_ON(page_block == 0); + + first_unmapped = page_block; + +page_is_mapped: + end_index = i_size >> PAGE_CACHE_SHIFT; + if (page->index >= end_index) { + /* + * The page straddles i_size. It must be zeroed out on each + * and every writepage invokation because it may be mmapped. + * "A file is mapped in multiples of the page size. For a file + * that is not a multiple of the page size, the remaining memory + * is zeroed when mapped, and writes to that region are not + * written out to the file." + */ + unsigned offset = i_size & (PAGE_CACHE_SIZE - 1); + char *kaddr; + + if (page->index > end_index || !offset) + goto confused; + kaddr = kmap_atomic(page, KM_USER0); + memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset); + flush_dcache_page(page); + kunmap_atomic(kaddr, KM_USER0); + } + + /* + * This page will go to BIO. Do we need to send this BIO off first? + */ + if (bio && *last_block_in_bio != blocks[0] - 1) + bio = mpage_bio_submit(WRITE, bio); + +alloc_new: + if (bio == NULL) { + bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), + bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH); + if (bio == NULL) + goto confused; + } + + /* + * Must try to add the page before marking the buffer clean or + * the confused fail path above (OOM) will be very confused when + * it finds all bh marked clean (i.e. it will not write anything) + */ + length = first_unmapped << blkbits; + if (bio_add_page(bio, page, length, 0) < length) { + bio = mpage_bio_submit(WRITE, bio); + goto alloc_new; + } + + /* + * 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); + + /* + * we cannot drop the bh if the page is not uptodate + * or a concurrent readpage would fail to serialize with the bh + * and it would read from disk before we reach the platter. + */ + if (buffer_heads_over_limit && PageUptodate(page)) + try_to_free_buffers(page); + } + + BUG_ON(PageWriteback(page)); + set_page_writeback(page); + unlock_page(page); + if (boundary || (first_unmapped != blocks_per_page)) { + bio = mpage_bio_submit(WRITE, bio); + if (boundary_block) { + write_boundary_block(boundary_bdev, + boundary_block, 1 << blkbits); + } + } else { + *last_block_in_bio = blocks[blocks_per_page - 1]; + } + goto out; + +confused: + if (bio) + bio = mpage_bio_submit(WRITE, bio); + + if (writepage_fn) { + *ret = (*writepage_fn)(page, wbc); + } else { + *ret = -EAGAIN; + goto out; + } + /* + * The caller has a ref on the inode, so *mapping is stable + */ + if (*ret) { + if (*ret == -ENOSPC) + set_bit(AS_ENOSPC, &mapping->flags); + else + set_bit(AS_EIO, &mapping->flags); + } +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 + * @wbc: subtract the number of written pages from *@wbc->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. + * + * 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 guarantee that all the data which was dirty at the time + * the call was made get new I/O started against them. If wbc->sync_mode is + * WB_SYNC_ALL then we were called for data integrity and we must wait for + * existing IO to complete. + */ +int +mpage_writepages(struct address_space *mapping, + struct writeback_control *wbc, get_block_t get_block) +{ + return __mpage_writepages(mapping, wbc, get_block, + mapping->a_ops->writepage); +} + +int +__mpage_writepages(struct address_space *mapping, + struct writeback_control *wbc, get_block_t get_block, + writepage_t writepage_fn) +{ + struct backing_dev_info *bdi = mapping->backing_dev_info; + struct bio *bio = NULL; + sector_t last_block_in_bio = 0; + int ret = 0; + int done = 0; + int (*writepage)(struct page *page, struct writeback_control *wbc); + struct pagevec pvec; + int nr_pages; + pgoff_t index; + pgoff_t end = -1; /* Inclusive */ + int scanned = 0; + int is_range = 0; + + if (wbc->nonblocking && bdi_write_congested(bdi)) { + wbc->encountered_congestion = 1; + return 0; + } + + writepage = NULL; + if (get_block == NULL) + writepage = mapping->a_ops->writepage; + + pagevec_init(&pvec, 0); + if (wbc->sync_mode == WB_SYNC_NONE) { + index = mapping->writeback_index; /* Start from prev offset */ + } else { + index = 0; /* whole-file sweep */ + scanned = 1; + } + if (wbc->start || wbc->end) { + index = wbc->start >> PAGE_CACHE_SHIFT; + end = wbc->end >> PAGE_CACHE_SHIFT; + is_range = 1; + scanned = 1; + } +retry: + while (!done && (index <= end) && + (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, + PAGECACHE_TAG_DIRTY, + min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) { + unsigned i; + + scanned = 1; + for (i = 0; i < nr_pages; i++) { + struct page *page = pvec.pages[i]; + + /* + * At this point we hold neither mapping->tree_lock nor + * lock on the page itself: the page may be truncated or + * invalidated (changing page->mapping to NULL), or even + * swizzled back from swapper_space to tmpfs file + * mapping + */ + + lock_page(page); + + if (unlikely(page->mapping != mapping)) { + unlock_page(page); + continue; + } + + if (unlikely(is_range) && page->index > end) { + done = 1; + unlock_page(page); + continue; + } + + if (wbc->sync_mode != WB_SYNC_NONE) + wait_on_page_writeback(page); + + if (PageWriteback(page) || + !clear_page_dirty_for_io(page)) { + unlock_page(page); + continue; + } + + if (writepage) { + ret = (*writepage)(page, wbc); + if (ret) { + if (ret == -ENOSPC) + set_bit(AS_ENOSPC, + &mapping->flags); + else + set_bit(AS_EIO, + &mapping->flags); + } + } else { + bio = __mpage_writepage(bio, page, get_block, + &last_block_in_bio, &ret, wbc, + writepage_fn); + } + if (ret || (--(wbc->nr_to_write) <= 0)) + done = 1; + if (wbc->nonblocking && bdi_write_congested(bdi)) { + wbc->encountered_congestion = 1; + done = 1; + } + } + pagevec_release(&pvec); + cond_resched(); + } + if (!scanned && !done) { + /* + * We hit the last page and there is more work to be done: wrap + * back to the start of the file + */ + scanned = 1; + index = 0; + goto retry; + } + if (!is_range) + mapping->writeback_index = index; + if (bio) + mpage_bio_submit(WRITE, bio); + return ret; +} +EXPORT_SYMBOL(mpage_writepages); +EXPORT_SYMBOL(__mpage_writepages); + +int mpage_writepage(struct page *page, get_block_t get_block, + struct writeback_control *wbc) +{ + int ret = 0; + struct bio *bio; + sector_t last_block_in_bio = 0; + + bio = __mpage_writepage(NULL, page, get_block, + &last_block_in_bio, &ret, wbc, NULL); + if (bio) + mpage_bio_submit(WRITE, bio); + + return ret; +} +EXPORT_SYMBOL(mpage_writepage); |