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Linux/mm/page_io.c

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  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/gfp.h>
 16 #include <linux/pagemap.h>
 17 #include <linux/swap.h>
 18 #include <linux/bio.h>
 19 #include <linux/swapops.h>
 20 #include <linux/buffer_head.h>
 21 #include <linux/writeback.h>
 22 #include <linux/frontswap.h>
 23 #include <linux/aio.h>
 24 #include <linux/blkdev.h>
 25 #include <asm/pgtable.h>
 26 
 27 static struct bio *get_swap_bio(gfp_t gfp_flags,
 28                                 struct page *page, bio_end_io_t end_io)
 29 {
 30         struct bio *bio;
 31 
 32         bio = bio_alloc(gfp_flags, 1);
 33         if (bio) {
 34                 bio->bi_sector = map_swap_page(page, &bio->bi_bdev);
 35                 bio->bi_sector <<= PAGE_SHIFT - 9;
 36                 bio->bi_io_vec[0].bv_page = page;
 37                 bio->bi_io_vec[0].bv_len = PAGE_SIZE;
 38                 bio->bi_io_vec[0].bv_offset = 0;
 39                 bio->bi_vcnt = 1;
 40                 bio->bi_size = PAGE_SIZE;
 41                 bio->bi_end_io = end_io;
 42         }
 43         return bio;
 44 }
 45 
 46 void end_swap_bio_write(struct bio *bio, int err)
 47 {
 48         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 49         struct page *page = bio->bi_io_vec[0].bv_page;
 50 
 51         if (!uptodate) {
 52                 SetPageError(page);
 53                 /*
 54                  * We failed to write the page out to swap-space.
 55                  * Re-dirty the page in order to avoid it being reclaimed.
 56                  * Also print a dire warning that things will go BAD (tm)
 57                  * very quickly.
 58                  *
 59                  * Also clear PG_reclaim to avoid rotate_reclaimable_page()
 60                  */
 61                 set_page_dirty(page);
 62                 printk(KERN_ALERT "Write-error on swap-device (%u:%u:%Lu)\n",
 63                                 imajor(bio->bi_bdev->bd_inode),
 64                                 iminor(bio->bi_bdev->bd_inode),
 65                                 (unsigned long long)bio->bi_sector);
 66                 ClearPageReclaim(page);
 67         }
 68         end_page_writeback(page);
 69         bio_put(bio);
 70 }
 71 
 72 void end_swap_bio_read(struct bio *bio, int err)
 73 {
 74         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 75         struct page *page = bio->bi_io_vec[0].bv_page;
 76 
 77         if (!uptodate) {
 78                 SetPageError(page);
 79                 ClearPageUptodate(page);
 80                 printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)\n",
 81                                 imajor(bio->bi_bdev->bd_inode),
 82                                 iminor(bio->bi_bdev->bd_inode),
 83                                 (unsigned long long)bio->bi_sector);
 84                 goto out;
 85         }
 86 
 87         SetPageUptodate(page);
 88 
 89         /*
 90          * There is no guarantee that the page is in swap cache - the software
 91          * suspend code (at least) uses end_swap_bio_read() against a non-
 92          * swapcache page.  So we must check PG_swapcache before proceeding with
 93          * this optimization.
 94          */
 95         if (likely(PageSwapCache(page))) {
 96                 struct swap_info_struct *sis;
 97 
 98                 sis = page_swap_info(page);
 99                 if (sis->flags & SWP_BLKDEV) {
100                         /*
101                          * The swap subsystem performs lazy swap slot freeing,
102                          * expecting that the page will be swapped out again.
103                          * So we can avoid an unnecessary write if the page
104                          * isn't redirtied.
105                          * This is good for real swap storage because we can
106                          * reduce unnecessary I/O and enhance wear-leveling
107                          * if an SSD is used as the as swap device.
108                          * But if in-memory swap device (eg zram) is used,
109                          * this causes a duplicated copy between uncompressed
110                          * data in VM-owned memory and compressed data in
111                          * zram-owned memory.  So let's free zram-owned memory
112                          * and make the VM-owned decompressed page *dirty*,
113                          * so the page should be swapped out somewhere again if
114                          * we again wish to reclaim it.
115                          */
116                         struct gendisk *disk = sis->bdev->bd_disk;
117                         if (disk->fops->swap_slot_free_notify) {
118                                 swp_entry_t entry;
119                                 unsigned long offset;
120 
121                                 entry.val = page_private(page);
122                                 offset = swp_offset(entry);
123 
124                                 SetPageDirty(page);
125                                 disk->fops->swap_slot_free_notify(sis->bdev,
126                                                 offset);
127                         }
128                 }
129         }
130 
131 out:
132         unlock_page(page);
133         bio_put(bio);
134 }
135 
136 int generic_swapfile_activate(struct swap_info_struct *sis,
137                                 struct file *swap_file,
138                                 sector_t *span)
139 {
140         struct address_space *mapping = swap_file->f_mapping;
141         struct inode *inode = mapping->host;
142         unsigned blocks_per_page;
143         unsigned long page_no;
144         unsigned blkbits;
145         sector_t probe_block;
146         sector_t last_block;
147         sector_t lowest_block = -1;
148         sector_t highest_block = 0;
149         int nr_extents = 0;
150         int ret;
151 
152         blkbits = inode->i_blkbits;
153         blocks_per_page = PAGE_SIZE >> blkbits;
154 
155         /*
156          * Map all the blocks into the extent list.  This code doesn't try
157          * to be very smart.
158          */
159         probe_block = 0;
160         page_no = 0;
161         last_block = i_size_read(inode) >> blkbits;
162         while ((probe_block + blocks_per_page) <= last_block &&
163                         page_no < sis->max) {
164                 unsigned block_in_page;
165                 sector_t first_block;
166 
167                 first_block = bmap(inode, probe_block);
168                 if (first_block == 0)
169                         goto bad_bmap;
170 
171                 /*
172                  * It must be PAGE_SIZE aligned on-disk
173                  */
174                 if (first_block & (blocks_per_page - 1)) {
175                         probe_block++;
176                         goto reprobe;
177                 }
178 
179                 for (block_in_page = 1; block_in_page < blocks_per_page;
180                                         block_in_page++) {
181                         sector_t block;
182 
183                         block = bmap(inode, probe_block + block_in_page);
184                         if (block == 0)
185                                 goto bad_bmap;
186                         if (block != first_block + block_in_page) {
187                                 /* Discontiguity */
188                                 probe_block++;
189                                 goto reprobe;
190                         }
191                 }
192 
193                 first_block >>= (PAGE_SHIFT - blkbits);
194                 if (page_no) {  /* exclude the header page */
195                         if (first_block < lowest_block)
196                                 lowest_block = first_block;
197                         if (first_block > highest_block)
198                                 highest_block = first_block;
199                 }
200 
201                 /*
202                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
203                  */
204                 ret = add_swap_extent(sis, page_no, 1, first_block);
205                 if (ret < 0)
206                         goto out;
207                 nr_extents += ret;
208                 page_no++;
209                 probe_block += blocks_per_page;
210 reprobe:
211                 continue;
212         }
213         ret = nr_extents;
214         *span = 1 + highest_block - lowest_block;
215         if (page_no == 0)
216                 page_no = 1;    /* force Empty message */
217         sis->max = page_no;
218         sis->pages = page_no - 1;
219         sis->highest_bit = page_no - 1;
220 out:
221         return ret;
222 bad_bmap:
223         printk(KERN_ERR "swapon: swapfile has holes\n");
224         ret = -EINVAL;
225         goto out;
226 }
227 
228 /*
229  * We may have stale swap cache pages in memory: notice
230  * them here and get rid of the unnecessary final write.
231  */
232 int swap_writepage(struct page *page, struct writeback_control *wbc)
233 {
234         int ret = 0;
235 
236         if (try_to_free_swap(page)) {
237                 unlock_page(page);
238                 goto out;
239         }
240         if (frontswap_store(page) == 0) {
241                 set_page_writeback(page);
242                 unlock_page(page);
243                 end_page_writeback(page);
244                 goto out;
245         }
246         ret = __swap_writepage(page, wbc, end_swap_bio_write);
247 out:
248         return ret;
249 }
250 
251 int __swap_writepage(struct page *page, struct writeback_control *wbc,
252         void (*end_write_func)(struct bio *, int))
253 {
254         struct bio *bio;
255         int ret = 0, rw = WRITE;
256         struct swap_info_struct *sis = page_swap_info(page);
257 
258         if (sis->flags & SWP_FILE) {
259                 struct kiocb kiocb;
260                 struct file *swap_file = sis->swap_file;
261                 struct address_space *mapping = swap_file->f_mapping;
262                 struct iovec iov = {
263                         .iov_base = kmap(page),
264                         .iov_len  = PAGE_SIZE,
265                 };
266 
267                 init_sync_kiocb(&kiocb, swap_file);
268                 kiocb.ki_pos = page_file_offset(page);
269                 kiocb.ki_nbytes = PAGE_SIZE;
270 
271                 set_page_writeback(page);
272                 unlock_page(page);
273                 ret = mapping->a_ops->direct_IO(KERNEL_WRITE,
274                                                 &kiocb, &iov,
275                                                 kiocb.ki_pos, 1);
276                 kunmap(page);
277                 if (ret == PAGE_SIZE) {
278                         count_vm_event(PSWPOUT);
279                         ret = 0;
280                 } else {
281                         /*
282                          * In the case of swap-over-nfs, this can be a
283                          * temporary failure if the system has limited
284                          * memory for allocating transmit buffers.
285                          * Mark the page dirty and avoid
286                          * rotate_reclaimable_page but rate-limit the
287                          * messages but do not flag PageError like
288                          * the normal direct-to-bio case as it could
289                          * be temporary.
290                          */
291                         set_page_dirty(page);
292                         ClearPageReclaim(page);
293                         pr_err_ratelimited("Write error on dio swapfile (%Lu)\n",
294                                 page_file_offset(page));
295                 }
296                 end_page_writeback(page);
297                 return ret;
298         }
299 
300         bio = get_swap_bio(GFP_NOIO, page, end_write_func);
301         if (bio == NULL) {
302                 set_page_dirty(page);
303                 unlock_page(page);
304                 ret = -ENOMEM;
305                 goto out;
306         }
307         if (wbc->sync_mode == WB_SYNC_ALL)
308                 rw |= REQ_SYNC;
309         count_vm_event(PSWPOUT);
310         set_page_writeback(page);
311         unlock_page(page);
312         submit_bio(rw, bio);
313 out:
314         return ret;
315 }
316 
317 int swap_readpage(struct page *page)
318 {
319         struct bio *bio;
320         int ret = 0;
321         struct swap_info_struct *sis = page_swap_info(page);
322 
323         VM_BUG_ON(!PageLocked(page));
324         VM_BUG_ON(PageUptodate(page));
325         if (frontswap_load(page) == 0) {
326                 SetPageUptodate(page);
327                 unlock_page(page);
328                 goto out;
329         }
330 
331         if (sis->flags & SWP_FILE) {
332                 struct file *swap_file = sis->swap_file;
333                 struct address_space *mapping = swap_file->f_mapping;
334 
335                 ret = mapping->a_ops->readpage(swap_file, page);
336                 if (!ret)
337                         count_vm_event(PSWPIN);
338                 return ret;
339         }
340 
341         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
342         if (bio == NULL) {
343                 unlock_page(page);
344                 ret = -ENOMEM;
345                 goto out;
346         }
347         count_vm_event(PSWPIN);
348         submit_bio(READ, bio);
349 out:
350         return ret;
351 }
352 
353 int swap_set_page_dirty(struct page *page)
354 {
355         struct swap_info_struct *sis = page_swap_info(page);
356 
357         if (sis->flags & SWP_FILE) {
358                 struct address_space *mapping = sis->swap_file->f_mapping;
359                 return mapping->a_ops->set_page_dirty(page);
360         } else {
361                 return __set_page_dirty_no_writeback(page);
362         }
363 }
364 

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