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47a191fd38
A block device driver may choose to provide a rw_page operation. These will be called when the filesystem is attempting to do page sized I/O to page cache pages (ie not for direct I/O). This does preclude I/Os that are larger than page size, so this may only be a performance gain for some devices. Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com> Tested-by: Dheeraj Reddy <dheeraj.reddy@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
716 lines
20 KiB
C
716 lines
20 KiB
C
/*
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* fs/mpage.c
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*
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* Copyright (C) 2002, Linus Torvalds.
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*
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* Contains functions related to preparing and submitting BIOs which contain
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* multiple pagecache pages.
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*
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* 15May2002 Andrew Morton
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* Initial version
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* 27Jun2002 axboe@suse.de
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* use bio_add_page() to build bio's just the right size
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*/
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/mm.h>
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#include <linux/kdev_t.h>
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#include <linux/gfp.h>
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#include <linux/bio.h>
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#include <linux/fs.h>
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#include <linux/buffer_head.h>
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#include <linux/blkdev.h>
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#include <linux/highmem.h>
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#include <linux/prefetch.h>
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#include <linux/mpage.h>
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#include <linux/writeback.h>
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#include <linux/backing-dev.h>
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#include <linux/pagevec.h>
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#include <linux/cleancache.h>
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/*
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* I/O completion handler for multipage BIOs.
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*
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* The mpage code never puts partial pages into a BIO (except for end-of-file).
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* If a page does not map to a contiguous run of blocks then it simply falls
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* back to block_read_full_page().
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*
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* Why is this? If a page's completion depends on a number of different BIOs
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* which can complete in any order (or at the same time) then determining the
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* status of that page is hard. See end_buffer_async_read() for the details.
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* There is no point in duplicating all that complexity.
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*/
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static void mpage_end_io(struct bio *bio, int err)
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{
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struct bio_vec *bv;
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int i;
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bio_for_each_segment_all(bv, bio, i) {
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struct page *page = bv->bv_page;
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page_endio(page, bio_data_dir(bio), err);
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}
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bio_put(bio);
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}
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static struct bio *mpage_bio_submit(int rw, struct bio *bio)
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{
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bio->bi_end_io = mpage_end_io;
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submit_bio(rw, bio);
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return NULL;
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}
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static struct bio *
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mpage_alloc(struct block_device *bdev,
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sector_t first_sector, int nr_vecs,
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gfp_t gfp_flags)
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{
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struct bio *bio;
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bio = bio_alloc(gfp_flags, nr_vecs);
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if (bio == NULL && (current->flags & PF_MEMALLOC)) {
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while (!bio && (nr_vecs /= 2))
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bio = bio_alloc(gfp_flags, nr_vecs);
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}
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if (bio) {
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bio->bi_bdev = bdev;
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bio->bi_iter.bi_sector = first_sector;
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}
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return bio;
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}
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/*
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* support function for mpage_readpages. The fs supplied get_block might
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* return an up to date buffer. This is used to map that buffer into
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* the page, which allows readpage to avoid triggering a duplicate call
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* to get_block.
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*
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* The idea is to avoid adding buffers to pages that don't already have
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* them. So when the buffer is up to date and the page size == block size,
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* this marks the page up to date instead of adding new buffers.
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*/
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static void
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map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
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{
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struct inode *inode = page->mapping->host;
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struct buffer_head *page_bh, *head;
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int block = 0;
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if (!page_has_buffers(page)) {
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/*
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* don't make any buffers if there is only one buffer on
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* the page and the page just needs to be set up to date
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*/
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if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
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buffer_uptodate(bh)) {
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SetPageUptodate(page);
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return;
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}
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create_empty_buffers(page, 1 << inode->i_blkbits, 0);
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}
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head = page_buffers(page);
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page_bh = head;
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do {
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if (block == page_block) {
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page_bh->b_state = bh->b_state;
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page_bh->b_bdev = bh->b_bdev;
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page_bh->b_blocknr = bh->b_blocknr;
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break;
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}
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page_bh = page_bh->b_this_page;
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block++;
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} while (page_bh != head);
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}
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/*
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* This is the worker routine which does all the work of mapping the disk
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* blocks and constructs largest possible bios, submits them for IO if the
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* blocks are not contiguous on the disk.
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*
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* We pass a buffer_head back and forth and use its buffer_mapped() flag to
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* represent the validity of its disk mapping and to decide when to do the next
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* get_block() call.
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*/
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static struct bio *
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do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
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sector_t *last_block_in_bio, struct buffer_head *map_bh,
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unsigned long *first_logical_block, get_block_t get_block)
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{
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struct inode *inode = page->mapping->host;
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const unsigned blkbits = inode->i_blkbits;
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const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
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const unsigned blocksize = 1 << blkbits;
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sector_t block_in_file;
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sector_t last_block;
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sector_t last_block_in_file;
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sector_t blocks[MAX_BUF_PER_PAGE];
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unsigned page_block;
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unsigned first_hole = blocks_per_page;
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struct block_device *bdev = NULL;
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int length;
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int fully_mapped = 1;
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unsigned nblocks;
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unsigned relative_block;
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if (page_has_buffers(page))
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goto confused;
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block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
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last_block = block_in_file + nr_pages * blocks_per_page;
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last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
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if (last_block > last_block_in_file)
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last_block = last_block_in_file;
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page_block = 0;
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/*
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* Map blocks using the result from the previous get_blocks call first.
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*/
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nblocks = map_bh->b_size >> blkbits;
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if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
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block_in_file < (*first_logical_block + nblocks)) {
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unsigned map_offset = block_in_file - *first_logical_block;
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unsigned last = nblocks - map_offset;
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for (relative_block = 0; ; relative_block++) {
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if (relative_block == last) {
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clear_buffer_mapped(map_bh);
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break;
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}
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if (page_block == blocks_per_page)
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break;
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blocks[page_block] = map_bh->b_blocknr + map_offset +
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relative_block;
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page_block++;
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block_in_file++;
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}
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bdev = map_bh->b_bdev;
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}
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/*
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* Then do more get_blocks calls until we are done with this page.
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*/
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map_bh->b_page = page;
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while (page_block < blocks_per_page) {
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map_bh->b_state = 0;
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map_bh->b_size = 0;
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if (block_in_file < last_block) {
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map_bh->b_size = (last_block-block_in_file) << blkbits;
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if (get_block(inode, block_in_file, map_bh, 0))
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goto confused;
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*first_logical_block = block_in_file;
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}
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if (!buffer_mapped(map_bh)) {
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fully_mapped = 0;
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if (first_hole == blocks_per_page)
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first_hole = page_block;
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page_block++;
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block_in_file++;
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continue;
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}
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/* some filesystems will copy data into the page during
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* the get_block call, in which case we don't want to
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* read it again. map_buffer_to_page copies the data
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* we just collected from get_block into the page's buffers
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* so readpage doesn't have to repeat the get_block call
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*/
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if (buffer_uptodate(map_bh)) {
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map_buffer_to_page(page, map_bh, page_block);
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goto confused;
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}
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if (first_hole != blocks_per_page)
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goto confused; /* hole -> non-hole */
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/* Contiguous blocks? */
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if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
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goto confused;
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nblocks = map_bh->b_size >> blkbits;
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for (relative_block = 0; ; relative_block++) {
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if (relative_block == nblocks) {
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clear_buffer_mapped(map_bh);
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break;
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} else if (page_block == blocks_per_page)
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break;
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blocks[page_block] = map_bh->b_blocknr+relative_block;
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page_block++;
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block_in_file++;
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}
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bdev = map_bh->b_bdev;
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}
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if (first_hole != blocks_per_page) {
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zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
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if (first_hole == 0) {
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SetPageUptodate(page);
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unlock_page(page);
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goto out;
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}
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} else if (fully_mapped) {
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SetPageMappedToDisk(page);
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}
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if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
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cleancache_get_page(page) == 0) {
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SetPageUptodate(page);
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goto confused;
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}
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/*
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* This page will go to BIO. Do we need to send this BIO off first?
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*/
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if (bio && (*last_block_in_bio != blocks[0] - 1))
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bio = mpage_bio_submit(READ, bio);
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alloc_new:
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if (bio == NULL) {
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if (first_hole == blocks_per_page) {
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if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
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page))
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goto out;
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}
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bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
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min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
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GFP_KERNEL);
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if (bio == NULL)
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goto confused;
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}
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length = first_hole << blkbits;
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if (bio_add_page(bio, page, length, 0) < length) {
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bio = mpage_bio_submit(READ, bio);
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goto alloc_new;
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}
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relative_block = block_in_file - *first_logical_block;
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nblocks = map_bh->b_size >> blkbits;
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if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
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(first_hole != blocks_per_page))
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bio = mpage_bio_submit(READ, bio);
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else
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*last_block_in_bio = blocks[blocks_per_page - 1];
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out:
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return bio;
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confused:
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if (bio)
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bio = mpage_bio_submit(READ, bio);
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if (!PageUptodate(page))
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block_read_full_page(page, get_block);
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else
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unlock_page(page);
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goto out;
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}
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/**
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* mpage_readpages - populate an address space with some pages & start reads against them
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* @mapping: the address_space
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* @pages: The address of a list_head which contains the target pages. These
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* pages have their ->index populated and are otherwise uninitialised.
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* The page at @pages->prev has the lowest file offset, and reads should be
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* issued in @pages->prev to @pages->next order.
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* @nr_pages: The number of pages at *@pages
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* @get_block: The filesystem's block mapper function.
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*
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* This function walks the pages and the blocks within each page, building and
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* emitting large BIOs.
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*
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* If anything unusual happens, such as:
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*
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* - encountering a page which has buffers
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* - encountering a page which has a non-hole after a hole
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* - encountering a page with non-contiguous blocks
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*
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* then this code just gives up and calls the buffer_head-based read function.
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* It does handle a page which has holes at the end - that is a common case:
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* the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
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*
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* BH_Boundary explanation:
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*
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* There is a problem. The mpage read code assembles several pages, gets all
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* their disk mappings, and then submits them all. That's fine, but obtaining
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* the disk mappings may require I/O. Reads of indirect blocks, for example.
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*
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* So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
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* submitted in the following order:
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* 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
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*
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* because the indirect block has to be read to get the mappings of blocks
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* 13,14,15,16. Obviously, this impacts performance.
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*
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* So what we do it to allow the filesystem's get_block() function to set
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* BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
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* after this one will require I/O against a block which is probably close to
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* this one. So you should push what I/O you have currently accumulated.
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*
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* This all causes the disk requests to be issued in the correct order.
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*/
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int
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mpage_readpages(struct address_space *mapping, struct list_head *pages,
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unsigned nr_pages, get_block_t get_block)
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{
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struct bio *bio = NULL;
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unsigned page_idx;
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sector_t last_block_in_bio = 0;
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struct buffer_head map_bh;
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unsigned long first_logical_block = 0;
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map_bh.b_state = 0;
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map_bh.b_size = 0;
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for (page_idx = 0; page_idx < nr_pages; page_idx++) {
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struct page *page = list_entry(pages->prev, struct page, lru);
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prefetchw(&page->flags);
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list_del(&page->lru);
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if (!add_to_page_cache_lru(page, mapping,
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page->index, GFP_KERNEL)) {
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bio = do_mpage_readpage(bio, page,
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nr_pages - page_idx,
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&last_block_in_bio, &map_bh,
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&first_logical_block,
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get_block);
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}
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page_cache_release(page);
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}
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BUG_ON(!list_empty(pages));
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if (bio)
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mpage_bio_submit(READ, bio);
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return 0;
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}
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EXPORT_SYMBOL(mpage_readpages);
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/*
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* This isn't called much at all
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*/
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int mpage_readpage(struct page *page, get_block_t get_block)
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{
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struct bio *bio = NULL;
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sector_t last_block_in_bio = 0;
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struct buffer_head map_bh;
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unsigned long first_logical_block = 0;
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map_bh.b_state = 0;
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map_bh.b_size = 0;
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bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
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&map_bh, &first_logical_block, get_block);
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if (bio)
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mpage_bio_submit(READ, bio);
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return 0;
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}
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EXPORT_SYMBOL(mpage_readpage);
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/*
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* Writing is not so simple.
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*
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* If the page has buffers then they will be used for obtaining the disk
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* mapping. We only support pages which are fully mapped-and-dirty, with a
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* special case for pages which are unmapped at the end: end-of-file.
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*
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* If the page has no buffers (preferred) then the page is mapped here.
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*
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* If all blocks are found to be contiguous then the page can go into the
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* BIO. Otherwise fall back to the mapping's writepage().
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*
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* FIXME: This code wants an estimate of how many pages are still to be
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* written, so it can intelligently allocate a suitably-sized BIO. For now,
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* just allocate full-size (16-page) BIOs.
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*/
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struct mpage_data {
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struct bio *bio;
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sector_t last_block_in_bio;
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get_block_t *get_block;
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unsigned use_writepage;
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};
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/*
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* We have our BIO, so we can now mark the buffers clean. Make
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* sure to only clean buffers which we know we'll be writing.
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*/
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static void clean_buffers(struct page *page, unsigned first_unmapped)
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{
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unsigned buffer_counter = 0;
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struct buffer_head *bh, *head;
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if (!page_has_buffers(page))
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return;
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head = page_buffers(page);
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bh = head;
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do {
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if (buffer_counter++ == first_unmapped)
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break;
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clear_buffer_dirty(bh);
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bh = bh->b_this_page;
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} while (bh != head);
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/*
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* we cannot drop the bh if the page is not uptodate or a concurrent
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* readpage would fail to serialize with the bh and it would read from
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* disk before we reach the platter.
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*/
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if (buffer_heads_over_limit && PageUptodate(page))
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try_to_free_buffers(page);
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}
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static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
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void *data)
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{
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struct mpage_data *mpd = data;
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struct bio *bio = mpd->bio;
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struct address_space *mapping = page->mapping;
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struct inode *inode = page->mapping->host;
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const unsigned blkbits = inode->i_blkbits;
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unsigned long end_index;
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const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
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sector_t last_block;
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sector_t block_in_file;
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sector_t blocks[MAX_BUF_PER_PAGE];
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unsigned page_block;
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unsigned first_unmapped = blocks_per_page;
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struct block_device *bdev = NULL;
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int boundary = 0;
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sector_t boundary_block = 0;
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struct block_device *boundary_bdev = NULL;
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int length;
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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);
|