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Linux/mm/page_io.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  linux/mm/page_io.c
  4  *
  5  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  6  *
  7  *  Swap reorganised 29.12.95, 
  8  *  Asynchronous swapping added 30.12.95. Stephen Tweedie
  9  *  Removed race in async swapping. 14.4.1996. Bruno Haible
 10  *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
 11  *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
 12  */
 13 
 14 #include <linux/mm.h>
 15 #include <linux/kernel_stat.h>
 16 #include <linux/gfp.h>
 17 #include <linux/pagemap.h>
 18 #include <linux/swap.h>
 19 #include <linux/bio.h>
 20 #include <linux/swapops.h>
 21 #include <linux/buffer_head.h>
 22 #include <linux/writeback.h>
 23 #include <linux/frontswap.h>
 24 #include <linux/blkdev.h>
 25 #include <linux/uio.h>
 26 #include <linux/sched/task.h>
 27 #include <asm/pgtable.h>
 28 
 29 static struct bio *get_swap_bio(gfp_t gfp_flags,
 30                                 struct page *page, bio_end_io_t end_io)
 31 {
 32         int i, nr = hpage_nr_pages(page);
 33         struct bio *bio;
 34 
 35         bio = bio_alloc(gfp_flags, nr);
 36         if (bio) {
 37                 struct block_device *bdev;
 38 
 39                 bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
 40                 bio_set_dev(bio, bdev);
 41                 bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
 42                 bio->bi_end_io = end_io;
 43 
 44                 for (i = 0; i < nr; i++)
 45                         bio_add_page(bio, page + i, PAGE_SIZE, 0);
 46                 VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr);
 47         }
 48         return bio;
 49 }
 50 
 51 void end_swap_bio_write(struct bio *bio)
 52 {
 53         struct page *page = bio_first_page_all(bio);
 54 
 55         if (bio->bi_status) {
 56                 SetPageError(page);
 57                 /*
 58                  * We failed to write the page out to swap-space.
 59                  * Re-dirty the page in order to avoid it being reclaimed.
 60                  * Also print a dire warning that things will go BAD (tm)
 61                  * very quickly.
 62                  *
 63                  * Also clear PG_reclaim to avoid rotate_reclaimable_page()
 64                  */
 65                 set_page_dirty(page);
 66                 pr_alert("Write-error on swap-device (%u:%u:%llu)\n",
 67                          MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
 68                          (unsigned long long)bio->bi_iter.bi_sector);
 69                 ClearPageReclaim(page);
 70         }
 71         end_page_writeback(page);
 72         bio_put(bio);
 73 }
 74 
 75 static void swap_slot_free_notify(struct page *page)
 76 {
 77         struct swap_info_struct *sis;
 78         struct gendisk *disk;
 79 
 80         /*
 81          * There is no guarantee that the page is in swap cache - the software
 82          * suspend code (at least) uses end_swap_bio_read() against a non-
 83          * swapcache page.  So we must check PG_swapcache before proceeding with
 84          * this optimization.
 85          */
 86         if (unlikely(!PageSwapCache(page)))
 87                 return;
 88 
 89         sis = page_swap_info(page);
 90         if (!(sis->flags & SWP_BLKDEV))
 91                 return;
 92 
 93         /*
 94          * The swap subsystem performs lazy swap slot freeing,
 95          * expecting that the page will be swapped out again.
 96          * So we can avoid an unnecessary write if the page
 97          * isn't redirtied.
 98          * This is good for real swap storage because we can
 99          * reduce unnecessary I/O and enhance wear-leveling
100          * if an SSD is used as the as swap device.
101          * But if in-memory swap device (eg zram) is used,
102          * this causes a duplicated copy between uncompressed
103          * data in VM-owned memory and compressed data in
104          * zram-owned memory.  So let's free zram-owned memory
105          * and make the VM-owned decompressed page *dirty*,
106          * so the page should be swapped out somewhere again if
107          * we again wish to reclaim it.
108          */
109         disk = sis->bdev->bd_disk;
110         if (disk->fops->swap_slot_free_notify) {
111                 swp_entry_t entry;
112                 unsigned long offset;
113 
114                 entry.val = page_private(page);
115                 offset = swp_offset(entry);
116 
117                 SetPageDirty(page);
118                 disk->fops->swap_slot_free_notify(sis->bdev,
119                                 offset);
120         }
121 }
122 
123 static void end_swap_bio_read(struct bio *bio)
124 {
125         struct page *page = bio_first_page_all(bio);
126         struct task_struct *waiter = bio->bi_private;
127 
128         if (bio->bi_status) {
129                 SetPageError(page);
130                 ClearPageUptodate(page);
131                 pr_alert("Read-error on swap-device (%u:%u:%llu)\n",
132                          MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
133                          (unsigned long long)bio->bi_iter.bi_sector);
134                 goto out;
135         }
136 
137         SetPageUptodate(page);
138         swap_slot_free_notify(page);
139 out:
140         unlock_page(page);
141         WRITE_ONCE(bio->bi_private, NULL);
142         bio_put(bio);
143         wake_up_process(waiter);
144         put_task_struct(waiter);
145 }
146 
147 int generic_swapfile_activate(struct swap_info_struct *sis,
148                                 struct file *swap_file,
149                                 sector_t *span)
150 {
151         struct address_space *mapping = swap_file->f_mapping;
152         struct inode *inode = mapping->host;
153         unsigned blocks_per_page;
154         unsigned long page_no;
155         unsigned blkbits;
156         sector_t probe_block;
157         sector_t last_block;
158         sector_t lowest_block = -1;
159         sector_t highest_block = 0;
160         int nr_extents = 0;
161         int ret;
162 
163         blkbits = inode->i_blkbits;
164         blocks_per_page = PAGE_SIZE >> blkbits;
165 
166         /*
167          * Map all the blocks into the extent list.  This code doesn't try
168          * to be very smart.
169          */
170         probe_block = 0;
171         page_no = 0;
172         last_block = i_size_read(inode) >> blkbits;
173         while ((probe_block + blocks_per_page) <= last_block &&
174                         page_no < sis->max) {
175                 unsigned block_in_page;
176                 sector_t first_block;
177 
178                 cond_resched();
179 
180                 first_block = bmap(inode, probe_block);
181                 if (first_block == 0)
182                         goto bad_bmap;
183 
184                 /*
185                  * It must be PAGE_SIZE aligned on-disk
186                  */
187                 if (first_block & (blocks_per_page - 1)) {
188                         probe_block++;
189                         goto reprobe;
190                 }
191 
192                 for (block_in_page = 1; block_in_page < blocks_per_page;
193                                         block_in_page++) {
194                         sector_t block;
195 
196                         block = bmap(inode, probe_block + block_in_page);
197                         if (block == 0)
198                                 goto bad_bmap;
199                         if (block != first_block + block_in_page) {
200                                 /* Discontiguity */
201                                 probe_block++;
202                                 goto reprobe;
203                         }
204                 }
205 
206                 first_block >>= (PAGE_SHIFT - blkbits);
207                 if (page_no) {  /* exclude the header page */
208                         if (first_block < lowest_block)
209                                 lowest_block = first_block;
210                         if (first_block > highest_block)
211                                 highest_block = first_block;
212                 }
213 
214                 /*
215                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
216                  */
217                 ret = add_swap_extent(sis, page_no, 1, first_block);
218                 if (ret < 0)
219                         goto out;
220                 nr_extents += ret;
221                 page_no++;
222                 probe_block += blocks_per_page;
223 reprobe:
224                 continue;
225         }
226         ret = nr_extents;
227         *span = 1 + highest_block - lowest_block;
228         if (page_no == 0)
229                 page_no = 1;    /* force Empty message */
230         sis->max = page_no;
231         sis->pages = page_no - 1;
232         sis->highest_bit = page_no - 1;
233 out:
234         return ret;
235 bad_bmap:
236         pr_err("swapon: swapfile has holes\n");
237         ret = -EINVAL;
238         goto out;
239 }
240 
241 /*
242  * We may have stale swap cache pages in memory: notice
243  * them here and get rid of the unnecessary final write.
244  */
245 int swap_writepage(struct page *page, struct writeback_control *wbc)
246 {
247         int ret = 0;
248 
249         if (try_to_free_swap(page)) {
250                 unlock_page(page);
251                 goto out;
252         }
253         if (frontswap_store(page) == 0) {
254                 set_page_writeback(page);
255                 unlock_page(page);
256                 end_page_writeback(page);
257                 goto out;
258         }
259         ret = __swap_writepage(page, wbc, end_swap_bio_write);
260 out:
261         return ret;
262 }
263 
264 static sector_t swap_page_sector(struct page *page)
265 {
266         return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
267 }
268 
269 static inline void count_swpout_vm_event(struct page *page)
270 {
271 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
272         if (unlikely(PageTransHuge(page)))
273                 count_vm_event(THP_SWPOUT);
274 #endif
275         count_vm_events(PSWPOUT, hpage_nr_pages(page));
276 }
277 
278 int __swap_writepage(struct page *page, struct writeback_control *wbc,
279                 bio_end_io_t end_write_func)
280 {
281         struct bio *bio;
282         int ret;
283         struct swap_info_struct *sis = page_swap_info(page);
284 
285         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
286         if (sis->flags & SWP_FILE) {
287                 struct kiocb kiocb;
288                 struct file *swap_file = sis->swap_file;
289                 struct address_space *mapping = swap_file->f_mapping;
290                 struct bio_vec bv = {
291                         .bv_page = page,
292                         .bv_len  = PAGE_SIZE,
293                         .bv_offset = 0
294                 };
295                 struct iov_iter from;
296 
297                 iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE);
298                 init_sync_kiocb(&kiocb, swap_file);
299                 kiocb.ki_pos = page_file_offset(page);
300 
301                 set_page_writeback(page);
302                 unlock_page(page);
303                 ret = mapping->a_ops->direct_IO(&kiocb, &from);
304                 if (ret == PAGE_SIZE) {
305                         count_vm_event(PSWPOUT);
306                         ret = 0;
307                 } else {
308                         /*
309                          * In the case of swap-over-nfs, this can be a
310                          * temporary failure if the system has limited
311                          * memory for allocating transmit buffers.
312                          * Mark the page dirty and avoid
313                          * rotate_reclaimable_page but rate-limit the
314                          * messages but do not flag PageError like
315                          * the normal direct-to-bio case as it could
316                          * be temporary.
317                          */
318                         set_page_dirty(page);
319                         ClearPageReclaim(page);
320                         pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
321                                            page_file_offset(page));
322                 }
323                 end_page_writeback(page);
324                 return ret;
325         }
326 
327         ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
328         if (!ret) {
329                 count_swpout_vm_event(page);
330                 return 0;
331         }
332 
333         ret = 0;
334         bio = get_swap_bio(GFP_NOIO, page, end_write_func);
335         if (bio == NULL) {
336                 set_page_dirty(page);
337                 unlock_page(page);
338                 ret = -ENOMEM;
339                 goto out;
340         }
341         bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
342         count_swpout_vm_event(page);
343         set_page_writeback(page);
344         unlock_page(page);
345         submit_bio(bio);
346 out:
347         return ret;
348 }
349 
350 int swap_readpage(struct page *page, bool synchronous)
351 {
352         struct bio *bio;
353         int ret = 0;
354         struct swap_info_struct *sis = page_swap_info(page);
355         blk_qc_t qc;
356         struct gendisk *disk;
357 
358         VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
359         VM_BUG_ON_PAGE(!PageLocked(page), page);
360         VM_BUG_ON_PAGE(PageUptodate(page), page);
361         if (frontswap_load(page) == 0) {
362                 SetPageUptodate(page);
363                 unlock_page(page);
364                 goto out;
365         }
366 
367         if (sis->flags & SWP_FILE) {
368                 struct file *swap_file = sis->swap_file;
369                 struct address_space *mapping = swap_file->f_mapping;
370 
371                 ret = mapping->a_ops->readpage(swap_file, page);
372                 if (!ret)
373                         count_vm_event(PSWPIN);
374                 return ret;
375         }
376 
377         ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
378         if (!ret) {
379                 if (trylock_page(page)) {
380                         swap_slot_free_notify(page);
381                         unlock_page(page);
382                 }
383 
384                 count_vm_event(PSWPIN);
385                 return 0;
386         }
387 
388         ret = 0;
389         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
390         if (bio == NULL) {
391                 unlock_page(page);
392                 ret = -ENOMEM;
393                 goto out;
394         }
395         disk = bio->bi_disk;
396         /*
397          * Keep this task valid during swap readpage because the oom killer may
398          * attempt to access it in the page fault retry time check.
399          */
400         get_task_struct(current);
401         bio->bi_private = current;
402         bio_set_op_attrs(bio, REQ_OP_READ, 0);
403         count_vm_event(PSWPIN);
404         bio_get(bio);
405         qc = submit_bio(bio);
406         while (synchronous) {
407                 set_current_state(TASK_UNINTERRUPTIBLE);
408                 if (!READ_ONCE(bio->bi_private))
409                         break;
410 
411                 if (!blk_poll(disk->queue, qc))
412                         break;
413         }
414         __set_current_state(TASK_RUNNING);
415         bio_put(bio);
416 
417 out:
418         return ret;
419 }
420 
421 int swap_set_page_dirty(struct page *page)
422 {
423         struct swap_info_struct *sis = page_swap_info(page);
424 
425         if (sis->flags & SWP_FILE) {
426                 struct address_space *mapping = sis->swap_file->f_mapping;
427 
428                 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
429                 return mapping->a_ops->set_page_dirty(page);
430         } else {
431                 return __set_page_dirty_no_writeback(page);
432         }
433 }
434 

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