page_io.c

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/*
 *  linux/mm/page_io.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Swap reorganised 29.12.95, 
 *  Asynchronous swapping added 30.12.95. Stephen Tweedie
 *  Removed race in async swapping. 14.4.1996. Bruno Haible
 *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
 *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
 */

#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/gfp.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/swapops.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/frontswap.h>
#include <asm/pgtable.h>

static struct bio *get_swap_bio(gfp_t gfp_flags,
                struct page *page, bio_end_io_t end_io)
{
    struct bio *bio;

    bio = bio_alloc(gfp_flags, 1);
    if (bio) {
        bio->bi_sector = map_swap_page(page, &bio->bi_bdev);
        bio->bi_sector <<= PAGE_SHIFT - 9;
        bio->bi_io_vec[0].bv_page = page;
        bio->bi_io_vec[0].bv_len = PAGE_SIZE;
        bio->bi_io_vec[0].bv_offset = 0;
        bio->bi_vcnt = 1;
        bio->bi_idx = 0;
        bio->bi_size = PAGE_SIZE;
        bio->bi_end_io = end_io;
    }
    return bio;
}

static void end_swap_bio_write(struct bio *bio, int err)
{
    const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
    struct page *page = bio->bi_io_vec[0].bv_page;

    if (!uptodate) {
        SetPageError(page);
        /*
         * We failed to write the page out to swap-space.
         * Re-dirty the page in order to avoid it being reclaimed.
         * Also print a dire warning that things will go BAD (tm)
         * very quickly.
         *
         * Also clear PG_reclaim to avoid rotate_reclaimable_page()
         */
        set_page_dirty(page);
        printk(KERN_ALERT "Write-error on swap-device (%u:%u:%Lu)\n",
                imajor(bio->bi_bdev->bd_inode),
                iminor(bio->bi_bdev->bd_inode),
                (unsigned long long)bio->bi_sector);
        ClearPageReclaim(page);
    }
    end_page_writeback(page);
    bio_put(bio);
}

void end_swap_bio_read(struct bio *bio, int err)
{
    const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
    struct page *page = bio->bi_io_vec[0].bv_page;

    if (!uptodate) {
        SetPageError(page);
        ClearPageUptodate(page);
        printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)\n",
                imajor(bio->bi_bdev->bd_inode),
                iminor(bio->bi_bdev->bd_inode),
                (unsigned long long)bio->bi_sector);
    } else {
        SetPageUptodate(page);
    }
    unlock_page(page);
    bio_put(bio);
}

int generic_swapfile_activate(struct swap_info_struct *sis,
                struct file *swap_file,
                sector_t *span)
{
    struct address_space *mapping = swap_file->f_mapping;
    struct inode *inode = mapping->host;
    unsigned blocks_per_page;
    unsigned long page_no;
    unsigned blkbits;
    sector_t probe_block;
    sector_t last_block;
    sector_t lowest_block = -1;
    sector_t highest_block = 0;
    int nr_extents = 0;
    int ret;

    blkbits = inode->i_blkbits;
    blocks_per_page = PAGE_SIZE >> blkbits;

    /*
     * Map all the blocks into the extent list.  This code doesn't try
     * to be very smart.
     */
    probe_block = 0;
    page_no = 0;
    last_block = i_size_read(inode) >> blkbits;
    while ((probe_block + blocks_per_page) <= last_block &&
            page_no < sis->max) {
        unsigned block_in_page;
        sector_t first_block;

        first_block = bmap(inode, probe_block);
        if (first_block == 0)
            goto bad_bmap;

        /*
         * It must be PAGE_SIZE aligned on-disk
         */
        if (first_block & (blocks_per_page - 1)) {
            probe_block++;
            goto reprobe;
        }

        for (block_in_page = 1; block_in_page < blocks_per_page;
                    block_in_page++) {
            sector_t block;

            block = bmap(inode, probe_block + block_in_page);
            if (block == 0)
                goto bad_bmap;
            if (block != first_block + block_in_page) {
                /* Discontiguity */
                probe_block++;
                goto reprobe;
            }
        }

        first_block >>= (PAGE_SHIFT - blkbits);
        if (page_no) {  /* exclude the header page */
            if (first_block < lowest_block)
                lowest_block = first_block;
            if (first_block > highest_block)
                highest_block = first_block;
        }

        /*
         * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
         */
        ret = add_swap_extent(sis, page_no, 1, first_block);
        if (ret < 0)
            goto out;
        nr_extents += ret;
        page_no++;
        probe_block += blocks_per_page;
reprobe:
        continue;
    }
    ret = nr_extents;
    *span = 1 + highest_block - lowest_block;
    if (page_no == 0)
        page_no = 1;    /* force Empty message */
    sis->max = page_no;
    sis->pages = page_no - 1;
    sis->highest_bit = page_no - 1;
out:
    return ret;
bad_bmap:
    printk(KERN_ERR "swapon: swapfile has holes\n");
    ret = -EINVAL;
    goto out;
}

/*
 * We may have stale swap cache pages in memory: notice
 * them here and get rid of the unnecessary final write.
 */
int swap_writepage(struct page *page, struct writeback_control *wbc)
{
    struct bio *bio;
    int ret = 0, rw = WRITE;
    struct swap_info_struct *sis = page_swap_info(page);

    if (try_to_free_swap(page)) {
        unlock_page(page);
        goto out;
    }
    if (frontswap_store(page) == 0) {
        set_page_writeback(page);
        unlock_page(page);
        end_page_writeback(page);
        goto out;
    }

    if (sis->flags & SWP_FILE) {
        struct kiocb kiocb;
        struct file *swap_file = sis->swap_file;
        struct address_space *mapping = swap_file->f_mapping;
        struct iovec iov = {
            .iov_base = kmap(page),
            .iov_len  = PAGE_SIZE,
        };

        init_sync_kiocb(&kiocb, swap_file);
        kiocb.ki_pos = page_file_offset(page);
        kiocb.ki_left = PAGE_SIZE;
        kiocb.ki_nbytes = PAGE_SIZE;

        unlock_page(page);
        ret = mapping->a_ops->direct_IO(KERNEL_WRITE,
                        &kiocb, &iov,
                        kiocb.ki_pos, 1);
        kunmap(page);
        if (ret == PAGE_SIZE) {
            count_vm_event(PSWPOUT);
            ret = 0;
        }
        return ret;
    }

    bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
    if (bio == NULL) {
        set_page_dirty(page);
        unlock_page(page);
        ret = -ENOMEM;
        goto out;
    }
    if (wbc->sync_mode == WB_SYNC_ALL)
        rw |= REQ_SYNC;
    count_vm_event(PSWPOUT);
    set_page_writeback(page);
    unlock_page(page);
    submit_bio(rw, bio);
out:
    return ret;
}

int swap_readpage(struct page *page)
{
    struct bio *bio;
    int ret = 0;
    struct swap_info_struct *sis = page_swap_info(page);

    VM_BUG_ON(!PageLocked(page));
    VM_BUG_ON(PageUptodate(page));
    if (frontswap_load(page) == 0) {
        SetPageUptodate(page);
        unlock_page(page);
        goto out;
    }

    if (sis->flags & SWP_FILE) {
        struct file *swap_file = sis->swap_file;
        struct address_space *mapping = swap_file->f_mapping;

        ret = mapping->a_ops->readpage(swap_file, page);
        if (!ret)
            count_vm_event(PSWPIN);
        return ret;
    }

    bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
    if (bio == NULL) {
        unlock_page(page);
        ret = -ENOMEM;
        goto out;
    }
    count_vm_event(PSWPIN);
    submit_bio(READ, bio);
out:
    return ret;
}

int swap_set_page_dirty(struct page *page)
{
    struct swap_info_struct *sis = page_swap_info(page);

    if (sis->flags & SWP_FILE) {
        struct address_space *mapping = sis->swap_file->f_mapping;
        return mapping->a_ops->set_page_dirty(page);
    } else {
        return __set_page_dirty_no_writeback(page);
    }
}