--- /dev/null
+/*
+ * fs/mpage.c
+ *
+ * Copyright (C) 2002, Linus Torvalds.
+ *
+ * Contains functions related to preparing and submitting BIOs which contain
+ * multiple pagecache pages.
+ *
+ * 15May2002 Andrew Morton
+ * Initial version
+ * 27Jun2002 axboe@suse.de
+ * use bio_add_page() to build bio's just the right size
+ */
+
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/kdev_t.h>
+#include <linux/gfp.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>
+#include <linux/cleancache.h>
+#include "internal.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 void mpage_end_io(struct bio *bio, int err)
+{
+ struct bio_vec *bv;
+ int i;
+
+ bio_for_each_segment_all(bv, bio, i) {
+ struct page *page = bv->bv_page;
+ page_endio(page, bio_data_dir(bio), err);
+ }
+
+ bio_put(bio);
+}
+
+static struct bio *mpage_bio_submit(int rw, struct bio *bio)
+{
+ bio->bi_end_io = mpage_end_io;
+ guard_bio_eod(rw, bio);
+ submit_bio(rw, bio);
+ return NULL;
+}
+
+static struct bio *
+mpage_alloc(struct block_device *bdev,
+ sector_t first_sector, int nr_vecs,
+ gfp_t 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_iter.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);
+}
+
+/*
+ * This is the worker routine which does all the work of mapping the disk
+ * blocks and constructs largest possible bios, submits them for IO if the
+ * blocks are not contiguous on the disk.
+ *
+ * We pass a buffer_head back and forth and use its buffer_mapped() flag to
+ * represent the validity of its disk mapping and to decide when to do the next
+ * get_block() call.
+ */
+static struct bio *
+do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
+ sector_t *last_block_in_bio, struct buffer_head *map_bh,
+ unsigned long *first_logical_block, 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 last_block_in_file;
+ sector_t blocks[MAX_BUF_PER_PAGE];
+ unsigned page_block;
+ unsigned first_hole = blocks_per_page;
+ struct block_device *bdev = NULL;
+ int length;
+ int fully_mapped = 1;
+ unsigned nblocks;
+ unsigned relative_block;
+
+ if (page_has_buffers(page))
+ goto confused;
+
+ block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
+ last_block = block_in_file + nr_pages * blocks_per_page;
+ last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
+ if (last_block > last_block_in_file)
+ last_block = last_block_in_file;
+ page_block = 0;
+
+ /*
+ * Map blocks using the result from the previous get_blocks call first.
+ */
+ nblocks = map_bh->b_size >> blkbits;
+ if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
+ block_in_file < (*first_logical_block + nblocks)) {
+ unsigned map_offset = block_in_file - *first_logical_block;
+ unsigned last = nblocks - map_offset;
+
+ for (relative_block = 0; ; relative_block++) {
+ if (relative_block == last) {
+ clear_buffer_mapped(map_bh);
+ break;
+ }
+ if (page_block == blocks_per_page)
+ break;
+ blocks[page_block] = map_bh->b_blocknr + map_offset +
+ relative_block;
+ page_block++;
+ block_in_file++;
+ }
+ bdev = map_bh->b_bdev;
+ }
+
+ /*
+ * Then do more get_blocks calls until we are done with this page.
+ */
+ map_bh->b_page = page;
+ while (page_block < blocks_per_page) {
+ map_bh->b_state = 0;
+ map_bh->b_size = 0;
+
+ if (block_in_file < last_block) {
+ map_bh->b_size = (last_block-block_in_file) << blkbits;
+ if (get_block(inode, block_in_file, map_bh, 0))
+ goto confused;
+ *first_logical_block = block_in_file;
+ }
+
+ if (!buffer_mapped(map_bh)) {
+ fully_mapped = 0;
+ if (first_hole == blocks_per_page)
+ first_hole = page_block;
+ page_block++;
+ block_in_file++;
+ 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(map_bh)) {
+ map_buffer_to_page(page, map_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] != map_bh->b_blocknr-1)
+ goto confused;
+ nblocks = map_bh->b_size >> blkbits;
+ for (relative_block = 0; ; relative_block++) {
+ if (relative_block == nblocks) {
+ clear_buffer_mapped(map_bh);
+ break;
+ } else if (page_block == blocks_per_page)
+ break;
+ blocks[page_block] = map_bh->b_blocknr+relative_block;
+ page_block++;
+ block_in_file++;
+ }
+ bdev = map_bh->b_bdev;
+ }
+
+ if (first_hole != blocks_per_page) {
+ zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
+ if (first_hole == 0) {
+ SetPageUptodate(page);
+ unlock_page(page);
+ goto out;
+ }
+ } else if (fully_mapped) {
+ SetPageMappedToDisk(page);
+ }
+
+ if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
+ cleancache_get_page(page) == 0) {
+ SetPageUptodate(page);
+ goto confused;
+ }
+
+ /*
+ * 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) {
+ if (first_hole == blocks_per_page) {
+ if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
+ page))
+ goto out;
+ }
+ 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;
+ }
+
+ relative_block = block_in_file - *first_logical_block;
+ nblocks = map_bh->b_size >> blkbits;
+ if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
+ (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;
+}
+
+/**
+ * mpage_readpages - populate an address space with some pages & 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.
+ */
+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 buffer_head map_bh;
+ unsigned long first_logical_block = 0;
+
+ map_bh.b_state = 0;
+ map_bh.b_size = 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_lru(page, mapping,
+ page->index, GFP_KERNEL)) {
+ bio = do_mpage_readpage(bio, page,
+ nr_pages - page_idx,
+ &last_block_in_bio, &map_bh,
+ &first_logical_block,
+ get_block);
+ }
+ page_cache_release(page);
+ }
+ 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;
+ struct buffer_head map_bh;
+ unsigned long first_logical_block = 0;
+
+ map_bh.b_state = 0;
+ map_bh.b_size = 0;
+ bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
+ &map_bh, &first_logical_block, 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.
+ */
+
+struct mpage_data {
+ struct bio *bio;
+ sector_t last_block_in_bio;
+ get_block_t *get_block;
+ unsigned use_writepage;
+};
+
+/*
+ * 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.
+ */
+static void clean_buffers(struct page *page, unsigned first_unmapped)
+{
+ unsigned buffer_counter = 0;
+ struct buffer_head *bh, *head;
+ if (!page_has_buffers(page))
+ return;
+ head = page_buffers(page);
+ bh = head;
+
+ 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);
+}
+
+static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
+ void *data)
+{
+ struct mpage_data *mpd = data;
+ struct bio *bio = mpd->bio;
+ 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);
+ int ret = 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);
+ 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 = (sector_t)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;
+ map_bh.b_size = 1 << blkbits;
+ if (mpd->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 invocation 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);
+
+ if (page->index > end_index || !offset)
+ goto confused;
+ zero_user_segment(page, offset, PAGE_CACHE_SIZE);
+ }
+
+ /*
+ * This page will go to BIO. Do we need to send this BIO off first?
+ */
+ if (bio && mpd->last_block_in_bio != blocks[0] - 1)
+ bio = mpage_bio_submit(WRITE, bio);
+
+alloc_new:
+ if (bio == NULL) {
+ if (first_unmapped == blocks_per_page) {
+ if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
+ page, wbc)) {
+ clean_buffers(page, first_unmapped);
+ goto out;
+ }
+ }
+ 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;
+ }
+
+ clean_buffers(page, first_unmapped);
+
+ 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 {
+ mpd->last_block_in_bio = blocks[blocks_per_page - 1];
+ }
+ goto out;
+
+confused:
+ if (bio)
+ bio = mpage_bio_submit(WRITE, bio);
+
+ if (mpd->use_writepage) {
+ ret = mapping->a_ops->writepage(page, wbc);
+ } else {
+ ret = -EAGAIN;
+ goto out;
+ }
+ /*
+ * The caller has a ref on the inode, so *mapping is stable
+ */
+ mapping_set_error(mapping, ret);
+out:
+ mpd->bio = bio;
+ return ret;
+}
+
+/**
+ * mpage_writepages - walk the list of dirty pages of the given address space & 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)
+{
+ struct blk_plug plug;
+ int ret;
+
+ blk_start_plug(&plug);
+
+ if (!get_block)
+ ret = generic_writepages(mapping, wbc);
+ else {
+ struct mpage_data mpd = {
+ .bio = NULL,
+ .last_block_in_bio = 0,
+ .get_block = get_block,
+ .use_writepage = 1,
+ };
+
+ ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
+ if (mpd.bio)
+ mpage_bio_submit(WRITE, mpd.bio);
+ }
+ blk_finish_plug(&plug);
+ return ret;
+}
+EXPORT_SYMBOL(mpage_writepages);
+
+int mpage_writepage(struct page *page, get_block_t get_block,
+ struct writeback_control *wbc)
+{
+ struct mpage_data mpd = {
+ .bio = NULL,
+ .last_block_in_bio = 0,
+ .get_block = get_block,
+ .use_writepage = 0,
+ };
+ int ret = __mpage_writepage(page, wbc, &mpd);
+ if (mpd.bio)
+ mpage_bio_submit(WRITE, mpd.bio);
+ return ret;
+}
+EXPORT_SYMBOL(mpage_writepage);
Code Review / kvmfornfv.git / blobdiff