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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/psi.h>
 26 #include <linux/uio.h>
 27 #include <linux/sched/task.h>
 28 
 29 void end_swap_bio_write(struct bio *bio)
 30 {
 31         struct page *page = bio_first_page_all(bio);
 32 
 33         if (bio->bi_status) {
 34                 SetPageError(page);
 35                 /*
 36                  * We failed to write the page out to swap-space.
 37                  * Re-dirty the page in order to avoid it being reclaimed.
 38                  * Also print a dire warning that things will go BAD (tm)
 39                  * very quickly.
 40                  *
 41                  * Also clear PG_reclaim to avoid folio_rotate_reclaimable()
 42                  */
 43                 set_page_dirty(page);
 44                 pr_alert_ratelimited("Write-error on swap-device (%u:%u:%llu)\n",
 45                                      MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
 46                                      (unsigned long long)bio->bi_iter.bi_sector);
 47                 ClearPageReclaim(page);
 48         }
 49         end_page_writeback(page);
 50         bio_put(bio);
 51 }
 52 
 53 static void swap_slot_free_notify(struct page *page)
 54 {
 55         struct swap_info_struct *sis;
 56         struct gendisk *disk;
 57         swp_entry_t entry;
 58 
 59         /*
 60          * There is no guarantee that the page is in swap cache - the software
 61          * suspend code (at least) uses end_swap_bio_read() against a non-
 62          * swapcache page.  So we must check PG_swapcache before proceeding with
 63          * this optimization.
 64          */
 65         if (unlikely(!PageSwapCache(page)))
 66                 return;
 67 
 68         sis = page_swap_info(page);
 69         if (data_race(!(sis->flags & SWP_BLKDEV)))
 70                 return;
 71 
 72         /*
 73          * The swap subsystem performs lazy swap slot freeing,
 74          * expecting that the page will be swapped out again.
 75          * So we can avoid an unnecessary write if the page
 76          * isn't redirtied.
 77          * This is good for real swap storage because we can
 78          * reduce unnecessary I/O and enhance wear-leveling
 79          * if an SSD is used as the as swap device.
 80          * But if in-memory swap device (eg zram) is used,
 81          * this causes a duplicated copy between uncompressed
 82          * data in VM-owned memory and compressed data in
 83          * zram-owned memory.  So let's free zram-owned memory
 84          * and make the VM-owned decompressed page *dirty*,
 85          * so the page should be swapped out somewhere again if
 86          * we again wish to reclaim it.
 87          */
 88         disk = sis->bdev->bd_disk;
 89         entry.val = page_private(page);
 90         if (disk->fops->swap_slot_free_notify && __swap_count(entry) == 1) {
 91                 unsigned long offset;
 92 
 93                 offset = swp_offset(entry);
 94 
 95                 SetPageDirty(page);
 96                 disk->fops->swap_slot_free_notify(sis->bdev,
 97                                 offset);
 98         }
 99 }
100 
101 static void end_swap_bio_read(struct bio *bio)
102 {
103         struct page *page = bio_first_page_all(bio);
104         struct task_struct *waiter = bio->bi_private;
105 
106         if (bio->bi_status) {
107                 SetPageError(page);
108                 ClearPageUptodate(page);
109                 pr_alert_ratelimited("Read-error on swap-device (%u:%u:%llu)\n",
110                                      MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
111                                      (unsigned long long)bio->bi_iter.bi_sector);
112                 goto out;
113         }
114 
115         SetPageUptodate(page);
116         swap_slot_free_notify(page);
117 out:
118         unlock_page(page);
119         WRITE_ONCE(bio->bi_private, NULL);
120         bio_put(bio);
121         if (waiter) {
122                 blk_wake_io_task(waiter);
123                 put_task_struct(waiter);
124         }
125 }
126 
127 int generic_swapfile_activate(struct swap_info_struct *sis,
128                                 struct file *swap_file,
129                                 sector_t *span)
130 {
131         struct address_space *mapping = swap_file->f_mapping;
132         struct inode *inode = mapping->host;
133         unsigned blocks_per_page;
134         unsigned long page_no;
135         unsigned blkbits;
136         sector_t probe_block;
137         sector_t last_block;
138         sector_t lowest_block = -1;
139         sector_t highest_block = 0;
140         int nr_extents = 0;
141         int ret;
142 
143         blkbits = inode->i_blkbits;
144         blocks_per_page = PAGE_SIZE >> blkbits;
145 
146         /*
147          * Map all the blocks into the extent tree.  This code doesn't try
148          * to be very smart.
149          */
150         probe_block = 0;
151         page_no = 0;
152         last_block = i_size_read(inode) >> blkbits;
153         while ((probe_block + blocks_per_page) <= last_block &&
154                         page_no < sis->max) {
155                 unsigned block_in_page;
156                 sector_t first_block;
157 
158                 cond_resched();
159 
160                 first_block = probe_block;
161                 ret = bmap(inode, &first_block);
162                 if (ret || !first_block)
163                         goto bad_bmap;
164 
165                 /*
166                  * It must be PAGE_SIZE aligned on-disk
167                  */
168                 if (first_block & (blocks_per_page - 1)) {
169                         probe_block++;
170                         goto reprobe;
171                 }
172 
173                 for (block_in_page = 1; block_in_page < blocks_per_page;
174                                         block_in_page++) {
175                         sector_t block;
176 
177                         block = probe_block + block_in_page;
178                         ret = bmap(inode, &block);
179                         if (ret || !block)
180                                 goto bad_bmap;
181 
182                         if (block != first_block + block_in_page) {
183                                 /* Discontiguity */
184                                 probe_block++;
185                                 goto reprobe;
186                         }
187                 }
188 
189                 first_block >>= (PAGE_SHIFT - blkbits);
190                 if (page_no) {  /* exclude the header page */
191                         if (first_block < lowest_block)
192                                 lowest_block = first_block;
193                         if (first_block > highest_block)
194                                 highest_block = first_block;
195                 }
196 
197                 /*
198                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
199                  */
200                 ret = add_swap_extent(sis, page_no, 1, first_block);
201                 if (ret < 0)
202                         goto out;
203                 nr_extents += ret;
204                 page_no++;
205                 probe_block += blocks_per_page;
206 reprobe:
207                 continue;
208         }
209         ret = nr_extents;
210         *span = 1 + highest_block - lowest_block;
211         if (page_no == 0)
212                 page_no = 1;    /* force Empty message */
213         sis->max = page_no;
214         sis->pages = page_no - 1;
215         sis->highest_bit = page_no - 1;
216 out:
217         return ret;
218 bad_bmap:
219         pr_err("swapon: swapfile has holes\n");
220         ret = -EINVAL;
221         goto out;
222 }
223 
224 /*
225  * We may have stale swap cache pages in memory: notice
226  * them here and get rid of the unnecessary final write.
227  */
228 int swap_writepage(struct page *page, struct writeback_control *wbc)
229 {
230         int ret = 0;
231 
232         if (try_to_free_swap(page)) {
233                 unlock_page(page);
234                 goto out;
235         }
236         /*
237          * Arch code may have to preserve more data than just the page
238          * contents, e.g. memory tags.
239          */
240         ret = arch_prepare_to_swap(page);
241         if (ret) {
242                 set_page_dirty(page);
243                 unlock_page(page);
244                 goto out;
245         }
246         if (frontswap_store(page) == 0) {
247                 set_page_writeback(page);
248                 unlock_page(page);
249                 end_page_writeback(page);
250                 goto out;
251         }
252         ret = __swap_writepage(page, wbc, end_swap_bio_write);
253 out:
254         return ret;
255 }
256 
257 static inline void count_swpout_vm_event(struct page *page)
258 {
259 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
260         if (unlikely(PageTransHuge(page)))
261                 count_vm_event(THP_SWPOUT);
262 #endif
263         count_vm_events(PSWPOUT, thp_nr_pages(page));
264 }
265 
266 #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
267 static void bio_associate_blkg_from_page(struct bio *bio, struct page *page)
268 {
269         struct cgroup_subsys_state *css;
270         struct mem_cgroup *memcg;
271 
272         memcg = page_memcg(page);
273         if (!memcg)
274                 return;
275 
276         rcu_read_lock();
277         css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
278         bio_associate_blkg_from_css(bio, css);
279         rcu_read_unlock();
280 }
281 #else
282 #define bio_associate_blkg_from_page(bio, page)         do { } while (0)
283 #endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */
284 
285 int __swap_writepage(struct page *page, struct writeback_control *wbc,
286                 bio_end_io_t end_write_func)
287 {
288         struct bio *bio;
289         int ret;
290         struct swap_info_struct *sis = page_swap_info(page);
291 
292         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
293         if (data_race(sis->flags & SWP_FS_OPS)) {
294                 struct kiocb kiocb;
295                 struct file *swap_file = sis->swap_file;
296                 struct address_space *mapping = swap_file->f_mapping;
297                 struct bio_vec bv = {
298                         .bv_page = page,
299                         .bv_len  = PAGE_SIZE,
300                         .bv_offset = 0
301                 };
302                 struct iov_iter from;
303 
304                 iov_iter_bvec(&from, WRITE, &bv, 1, PAGE_SIZE);
305                 init_sync_kiocb(&kiocb, swap_file);
306                 kiocb.ki_pos = page_file_offset(page);
307 
308                 set_page_writeback(page);
309                 unlock_page(page);
310                 ret = mapping->a_ops->direct_IO(&kiocb, &from);
311                 if (ret == PAGE_SIZE) {
312                         count_vm_event(PSWPOUT);
313                         ret = 0;
314                 } else {
315                         /*
316                          * In the case of swap-over-nfs, this can be a
317                          * temporary failure if the system has limited
318                          * memory for allocating transmit buffers.
319                          * Mark the page dirty and avoid
320                          * folio_rotate_reclaimable but rate-limit the
321                          * messages but do not flag PageError like
322                          * the normal direct-to-bio case as it could
323                          * be temporary.
324                          */
325                         set_page_dirty(page);
326                         ClearPageReclaim(page);
327                         pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
328                                            page_file_offset(page));
329                 }
330                 end_page_writeback(page);
331                 return ret;
332         }
333 
334         ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
335         if (!ret) {
336                 count_swpout_vm_event(page);
337                 return 0;
338         }
339 
340         bio = bio_alloc(GFP_NOIO, 1);
341         bio_set_dev(bio, sis->bdev);
342         bio->bi_iter.bi_sector = swap_page_sector(page);
343         bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
344         bio->bi_end_io = end_write_func;
345         bio_add_page(bio, page, thp_size(page), 0);
346 
347         bio_associate_blkg_from_page(bio, page);
348         count_swpout_vm_event(page);
349         set_page_writeback(page);
350         unlock_page(page);
351         submit_bio(bio);
352 
353         return 0;
354 }
355 
356 int swap_readpage(struct page *page, bool synchronous)
357 {
358         struct bio *bio;
359         int ret = 0;
360         struct swap_info_struct *sis = page_swap_info(page);
361         unsigned long pflags;
362 
363         VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
364         VM_BUG_ON_PAGE(!PageLocked(page), page);
365         VM_BUG_ON_PAGE(PageUptodate(page), page);
366 
367         /*
368          * Count submission time as memory stall. When the device is congested,
369          * or the submitting cgroup IO-throttled, submission can be a
370          * significant part of overall IO time.
371          */
372         psi_memstall_enter(&pflags);
373 
374         if (frontswap_load(page) == 0) {
375                 SetPageUptodate(page);
376                 unlock_page(page);
377                 goto out;
378         }
379 
380         if (data_race(sis->flags & SWP_FS_OPS)) {
381                 struct file *swap_file = sis->swap_file;
382                 struct address_space *mapping = swap_file->f_mapping;
383 
384                 ret = mapping->a_ops->readpage(swap_file, page);
385                 if (!ret)
386                         count_vm_event(PSWPIN);
387                 goto out;
388         }
389 
390         if (sis->flags & SWP_SYNCHRONOUS_IO) {
391                 ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
392                 if (!ret) {
393                         if (trylock_page(page)) {
394                                 swap_slot_free_notify(page);
395                                 unlock_page(page);
396                         }
397 
398                         count_vm_event(PSWPIN);
399                         goto out;
400                 }
401         }
402 
403         ret = 0;
404         bio = bio_alloc(GFP_KERNEL, 1);
405         bio_set_dev(bio, sis->bdev);
406         bio->bi_opf = REQ_OP_READ;
407         bio->bi_iter.bi_sector = swap_page_sector(page);
408         bio->bi_end_io = end_swap_bio_read;
409         bio_add_page(bio, page, thp_size(page), 0);
410         /*
411          * Keep this task valid during swap readpage because the oom killer may
412          * attempt to access it in the page fault retry time check.
413          */
414         if (synchronous) {
415                 bio->bi_opf |= REQ_POLLED;
416                 get_task_struct(current);
417                 bio->bi_private = current;
418         }
419         count_vm_event(PSWPIN);
420         bio_get(bio);
421         submit_bio(bio);
422         while (synchronous) {
423                 set_current_state(TASK_UNINTERRUPTIBLE);
424                 if (!READ_ONCE(bio->bi_private))
425                         break;
426 
427                 if (!bio_poll(bio, NULL, 0))
428                         blk_io_schedule();
429         }
430         __set_current_state(TASK_RUNNING);
431         bio_put(bio);
432 
433 out:
434         psi_memstall_leave(&pflags);
435         return ret;
436 }
437 
438 int swap_set_page_dirty(struct page *page)
439 {
440         struct swap_info_struct *sis = page_swap_info(page);
441 
442         if (data_race(sis->flags & SWP_FS_OPS)) {
443                 struct address_space *mapping = sis->swap_file->f_mapping;
444 
445                 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
446                 return mapping->a_ops->set_page_dirty(page);
447         } else {
448                 return __set_page_dirty_no_writeback(page);
449         }
450 }
451 

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