mm/page_io.c

   1 /*
   2  *  linux/mm/page_io.c
   3  *
   4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5  *
   6  *  Swap reorganised 29.12.95,
   7  *  Asynchronous swapping added 30.12.95. Stephen Tweedie
   8  *  Removed race in async swapping. 14.4.1996. Bruno Haible
   9  *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
  10  *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
  11  */
  12
  13 #include <linux/mm.h>
  14 #include <linux/kernel_stat.h>
  15 #include <linux/pagemap.h>
  16 #include <linux/swap.h>
  17 #include <linux/bio.h>
  18 #include <linux/swapops.h>
  19 #include <linux/buffer_head.h>  /* for block_sync_page() */
  20 #include <linux/mpage.h>
  21 #include <asm/pgtable.h>
  22
  23 static struct bio *
  24 get_swap_bio(int gfp_flags, struct page *page, bio_end_io_t end_io)
  25 {
  26         struct bio *bio;
  27
  28         bio = bio_alloc(gfp_flags, 1);
  29         if (bio) {
  30                 struct swap_info_struct *sis;
  31                 swp_entry_t entry;
  32
  33                 entry.val = page->index;
  34                 sis = get_swap_info_struct(swp_type(entry));
  35
  36                 bio->bi_sector = map_swap_page(sis, swp_offset(entry)) *
  37                                         (PAGE_SIZE >> 9);
  38                 bio->bi_bdev = sis->bdev;
  39                 bio->bi_io_vec[0].bv_page = page;
  40                 bio->bi_io_vec[0].bv_len = PAGE_SIZE;
  41                 bio->bi_io_vec[0].bv_offset = 0;
  42                 bio->bi_vcnt = 1;
  43                 bio->bi_idx = 0;
  44                 bio->bi_size = PAGE_SIZE;
  45                 bio->bi_end_io = end_io;
  46         }
  47         return bio;
  48 }
  49
  50 static int end_swap_bio_write(struct bio *bio, unsigned int bytes_done, int err)
  51 {
  52         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  53         struct page *page = bio->bi_io_vec[0].bv_page;
  54
  55         if (bio->bi_size)
  56                 return 1;
  57
  58         if (!uptodate)
  59                 SetPageError(page);
  60         end_page_writeback(page);
  61         bio_put(bio);
  62         return 0;
  63 }
  64
  65 static int end_swap_bio_read(struct bio *bio, unsigned int bytes_done, int err)
  66 {
  67         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  68         struct page *page = bio->bi_io_vec[0].bv_page;
  69
  70         if (bio->bi_size)
  71                 return 1;
  72
  73         if (!uptodate) {
  74                 SetPageError(page);
  75                 ClearPageUptodate(page);
  76         } else {
  77                 SetPageUptodate(page);
  78         }
  79         unlock_page(page);
  80         bio_put(bio);
  81         return 0;
  82 }
  83
  84 /*
  85  * We may have stale swap cache pages in memory: notice
  86  * them here and get rid of the unnecessary final write.
  87  */
  88 int swap_writepage(struct page *page)
  89 {
  90         struct bio *bio;
  91         int ret = 0;
  92
  93         if (remove_exclusive_swap_page(page)) {
  94                 unlock_page(page);
  95                 goto out;
  96         }
  97         bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
  98         if (bio == NULL) {
  99                 set_page_dirty(page);
 100                 ret = -ENOMEM;
 101                 goto out;
 102         }
 103         inc_page_state(pswpout);
 104         SetPageWriteback(page);
 105         unlock_page(page);
 106         submit_bio(WRITE, bio);
 107 out:
 108         return ret;
 109 }
 110
 111 int swap_readpage(struct file *file, struct page *page)
 112 {
 113         struct bio *bio;
 114         int ret = 0;
 115
 116         ClearPageUptodate(page);
 117         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
 118         if (bio == NULL) {
 119                 ret = -ENOMEM;
 120                 goto out;
 121         }
 122         inc_page_state(pswpin);
 123         submit_bio(READ, bio);
 124 out:
 125         return ret;
 126 }
 127 /*
 128  * swapper_space doesn't have a real inode, so it gets a special vm_writeback()
 129  * so we don't need swap special cases in generic_vm_writeback().
 130  *
 131  * Swap pages are !PageLocked and PageWriteback while under writeout so that
 132  * memory allocators will throttle against them.
 133  */
 134 static int swap_vm_writeback(struct page *page, struct writeback_control *wbc)
 135 {
 136         struct address_space *mapping = page->mapping;
 137
 138         unlock_page(page);
 139         return generic_writepages(mapping, wbc);
 140 }
 141
 142 struct address_space_operations swap_aops = {
 143         .vm_writeback   = swap_vm_writeback,
 144         .writepage      = swap_writepage,
 145         .readpage       = swap_readpage,
 146         .sync_page      = block_sync_page,
 147         .set_page_dirty = __set_page_dirty_nobuffers,
 148 };
 149
 150 /*
 151  * A scruffy utility function to read or write an arbitrary swap page
 152  * and wait on the I/O.
 153  */
 154 int rw_swap_page_sync(int rw, swp_entry_t entry, struct page *page)
 155 {
 156         int ret;
 157
 158         lock_page(page);
 159
 160         BUG_ON(page->mapping);
 161         page->mapping = &swapper_space;
 162         page->index = entry.val;
 163
 164         if (rw == READ) {
 165                 ret = swap_readpage(NULL, page);
 166                 wait_on_page_locked(page);
 167         } else {
 168                 ret = swap_writepage(page);
 169                 wait_on_page_writeback(page);
 170         }
 171         page->mapping = NULL;
 172         if (ret == 0 && (!PageUptodate(page) || PageError(page)))
 173                 ret = -EIO;
 174         return ret;
 175 }