swapin needs gfp_mask for loop on tmpfs
[linux-2.6.git] / mm / swapfile.c
1 /*
2  *  linux/mm/swapfile.c
3  *
4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5  *  Swap reorganised 29.12.95, Stephen Tweedie
6  */
7
8 #include <linux/mm.h>
9 #include <linux/hugetlb.h>
10 #include <linux/mman.h>
11 #include <linux/slab.h>
12 #include <linux/kernel_stat.h>
13 #include <linux/swap.h>
14 #include <linux/vmalloc.h>
15 #include <linux/pagemap.h>
16 #include <linux/namei.h>
17 #include <linux/shm.h>
18 #include <linux/blkdev.h>
19 #include <linux/writeback.h>
20 #include <linux/proc_fs.h>
21 #include <linux/seq_file.h>
22 #include <linux/init.h>
23 #include <linux/module.h>
24 #include <linux/rmap.h>
25 #include <linux/security.h>
26 #include <linux/backing-dev.h>
27 #include <linux/mutex.h>
28 #include <linux/capability.h>
29 #include <linux/syscalls.h>
30
31 #include <asm/pgtable.h>
32 #include <asm/tlbflush.h>
33 #include <linux/swapops.h>
34
35 DEFINE_SPINLOCK(swap_lock);
36 unsigned int nr_swapfiles;
37 long total_swap_pages;
38 static int swap_overflow;
39
40 static const char Bad_file[] = "Bad swap file entry ";
41 static const char Unused_file[] = "Unused swap file entry ";
42 static const char Bad_offset[] = "Bad swap offset entry ";
43 static const char Unused_offset[] = "Unused swap offset entry ";
44
45 struct swap_list_t swap_list = {-1, -1};
46
47 static struct swap_info_struct swap_info[MAX_SWAPFILES];
48
49 static DEFINE_MUTEX(swapon_mutex);
50
51 /*
52  * We need this because the bdev->unplug_fn can sleep and we cannot
53  * hold swap_lock while calling the unplug_fn. And swap_lock
54  * cannot be turned into a mutex.
55  */
56 static DECLARE_RWSEM(swap_unplug_sem);
57
58 void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
59 {
60         swp_entry_t entry;
61
62         down_read(&swap_unplug_sem);
63         entry.val = page_private(page);
64         if (PageSwapCache(page)) {
65                 struct block_device *bdev = swap_info[swp_type(entry)].bdev;
66                 struct backing_dev_info *bdi;
67
68                 /*
69                  * If the page is removed from swapcache from under us (with a
70                  * racy try_to_unuse/swapoff) we need an additional reference
71                  * count to avoid reading garbage from page_private(page) above.
72                  * If the WARN_ON triggers during a swapoff it maybe the race
73                  * condition and it's harmless. However if it triggers without
74                  * swapoff it signals a problem.
75                  */
76                 WARN_ON(page_count(page) <= 1);
77
78                 bdi = bdev->bd_inode->i_mapping->backing_dev_info;
79                 blk_run_backing_dev(bdi, page);
80         }
81         up_read(&swap_unplug_sem);
82 }
83
84 #define SWAPFILE_CLUSTER        256
85 #define LATENCY_LIMIT           256
86
87 static inline unsigned long scan_swap_map(struct swap_info_struct *si)
88 {
89         unsigned long offset, last_in_cluster;
90         int latency_ration = LATENCY_LIMIT;
91
92         /* 
93          * We try to cluster swap pages by allocating them sequentially
94          * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
95          * way, however, we resort to first-free allocation, starting
96          * a new cluster.  This prevents us from scattering swap pages
97          * all over the entire swap partition, so that we reduce
98          * overall disk seek times between swap pages.  -- sct
99          * But we do now try to find an empty cluster.  -Andrea
100          */
101
102         si->flags += SWP_SCANNING;
103         if (unlikely(!si->cluster_nr)) {
104                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
105                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER)
106                         goto lowest;
107                 spin_unlock(&swap_lock);
108
109                 offset = si->lowest_bit;
110                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
111
112                 /* Locate the first empty (unaligned) cluster */
113                 for (; last_in_cluster <= si->highest_bit; offset++) {
114                         if (si->swap_map[offset])
115                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
116                         else if (offset == last_in_cluster) {
117                                 spin_lock(&swap_lock);
118                                 si->cluster_next = offset-SWAPFILE_CLUSTER+1;
119                                 goto cluster;
120                         }
121                         if (unlikely(--latency_ration < 0)) {
122                                 cond_resched();
123                                 latency_ration = LATENCY_LIMIT;
124                         }
125                 }
126                 spin_lock(&swap_lock);
127                 goto lowest;
128         }
129
130         si->cluster_nr--;
131 cluster:
132         offset = si->cluster_next;
133         if (offset > si->highest_bit)
134 lowest:         offset = si->lowest_bit;
135 checks: if (!(si->flags & SWP_WRITEOK))
136                 goto no_page;
137         if (!si->highest_bit)
138                 goto no_page;
139         if (!si->swap_map[offset]) {
140                 if (offset == si->lowest_bit)
141                         si->lowest_bit++;
142                 if (offset == si->highest_bit)
143                         si->highest_bit--;
144                 si->inuse_pages++;
145                 if (si->inuse_pages == si->pages) {
146                         si->lowest_bit = si->max;
147                         si->highest_bit = 0;
148                 }
149                 si->swap_map[offset] = 1;
150                 si->cluster_next = offset + 1;
151                 si->flags -= SWP_SCANNING;
152                 return offset;
153         }
154
155         spin_unlock(&swap_lock);
156         while (++offset <= si->highest_bit) {
157                 if (!si->swap_map[offset]) {
158                         spin_lock(&swap_lock);
159                         goto checks;
160                 }
161                 if (unlikely(--latency_ration < 0)) {
162                         cond_resched();
163                         latency_ration = LATENCY_LIMIT;
164                 }
165         }
166         spin_lock(&swap_lock);
167         goto lowest;
168
169 no_page:
170         si->flags -= SWP_SCANNING;
171         return 0;
172 }
173
174 swp_entry_t get_swap_page(void)
175 {
176         struct swap_info_struct *si;
177         pgoff_t offset;
178         int type, next;
179         int wrapped = 0;
180
181         spin_lock(&swap_lock);
182         if (nr_swap_pages <= 0)
183                 goto noswap;
184         nr_swap_pages--;
185
186         for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
187                 si = swap_info + type;
188                 next = si->next;
189                 if (next < 0 ||
190                     (!wrapped && si->prio != swap_info[next].prio)) {
191                         next = swap_list.head;
192                         wrapped++;
193                 }
194
195                 if (!si->highest_bit)
196                         continue;
197                 if (!(si->flags & SWP_WRITEOK))
198                         continue;
199
200                 swap_list.next = next;
201                 offset = scan_swap_map(si);
202                 if (offset) {
203                         spin_unlock(&swap_lock);
204                         return swp_entry(type, offset);
205                 }
206                 next = swap_list.next;
207         }
208
209         nr_swap_pages++;
210 noswap:
211         spin_unlock(&swap_lock);
212         return (swp_entry_t) {0};
213 }
214
215 swp_entry_t get_swap_page_of_type(int type)
216 {
217         struct swap_info_struct *si;
218         pgoff_t offset;
219
220         spin_lock(&swap_lock);
221         si = swap_info + type;
222         if (si->flags & SWP_WRITEOK) {
223                 nr_swap_pages--;
224                 offset = scan_swap_map(si);
225                 if (offset) {
226                         spin_unlock(&swap_lock);
227                         return swp_entry(type, offset);
228                 }
229                 nr_swap_pages++;
230         }
231         spin_unlock(&swap_lock);
232         return (swp_entry_t) {0};
233 }
234
235 static struct swap_info_struct * swap_info_get(swp_entry_t entry)
236 {
237         struct swap_info_struct * p;
238         unsigned long offset, type;
239
240         if (!entry.val)
241                 goto out;
242         type = swp_type(entry);
243         if (type >= nr_swapfiles)
244                 goto bad_nofile;
245         p = & swap_info[type];
246         if (!(p->flags & SWP_USED))
247                 goto bad_device;
248         offset = swp_offset(entry);
249         if (offset >= p->max)
250                 goto bad_offset;
251         if (!p->swap_map[offset])
252                 goto bad_free;
253         spin_lock(&swap_lock);
254         return p;
255
256 bad_free:
257         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
258         goto out;
259 bad_offset:
260         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
261         goto out;
262 bad_device:
263         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
264         goto out;
265 bad_nofile:
266         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
267 out:
268         return NULL;
269 }       
270
271 static int swap_entry_free(struct swap_info_struct *p, unsigned long offset)
272 {
273         int count = p->swap_map[offset];
274
275         if (count < SWAP_MAP_MAX) {
276                 count--;
277                 p->swap_map[offset] = count;
278                 if (!count) {
279                         if (offset < p->lowest_bit)
280                                 p->lowest_bit = offset;
281                         if (offset > p->highest_bit)
282                                 p->highest_bit = offset;
283                         if (p->prio > swap_info[swap_list.next].prio)
284                                 swap_list.next = p - swap_info;
285                         nr_swap_pages++;
286                         p->inuse_pages--;
287                 }
288         }
289         return count;
290 }
291
292 /*
293  * Caller has made sure that the swapdevice corresponding to entry
294  * is still around or has not been recycled.
295  */
296 void swap_free(swp_entry_t entry)
297 {
298         struct swap_info_struct * p;
299
300         p = swap_info_get(entry);
301         if (p) {
302                 swap_entry_free(p, swp_offset(entry));
303                 spin_unlock(&swap_lock);
304         }
305 }
306
307 /*
308  * How many references to page are currently swapped out?
309  */
310 static inline int page_swapcount(struct page *page)
311 {
312         int count = 0;
313         struct swap_info_struct *p;
314         swp_entry_t entry;
315
316         entry.val = page_private(page);
317         p = swap_info_get(entry);
318         if (p) {
319                 /* Subtract the 1 for the swap cache itself */
320                 count = p->swap_map[swp_offset(entry)] - 1;
321                 spin_unlock(&swap_lock);
322         }
323         return count;
324 }
325
326 /*
327  * We can use this swap cache entry directly
328  * if there are no other references to it.
329  */
330 int can_share_swap_page(struct page *page)
331 {
332         int count;
333
334         BUG_ON(!PageLocked(page));
335         count = page_mapcount(page);
336         if (count <= 1 && PageSwapCache(page))
337                 count += page_swapcount(page);
338         return count == 1;
339 }
340
341 /*
342  * Work out if there are any other processes sharing this
343  * swap cache page. Free it if you can. Return success.
344  */
345 int remove_exclusive_swap_page(struct page *page)
346 {
347         int retval;
348         struct swap_info_struct * p;
349         swp_entry_t entry;
350
351         BUG_ON(PagePrivate(page));
352         BUG_ON(!PageLocked(page));
353
354         if (!PageSwapCache(page))
355                 return 0;
356         if (PageWriteback(page))
357                 return 0;
358         if (page_count(page) != 2) /* 2: us + cache */
359                 return 0;
360
361         entry.val = page_private(page);
362         p = swap_info_get(entry);
363         if (!p)
364                 return 0;
365
366         /* Is the only swap cache user the cache itself? */
367         retval = 0;
368         if (p->swap_map[swp_offset(entry)] == 1) {
369                 /* Recheck the page count with the swapcache lock held.. */
370                 write_lock_irq(&swapper_space.tree_lock);
371                 if ((page_count(page) == 2) && !PageWriteback(page)) {
372                         __delete_from_swap_cache(page);
373                         SetPageDirty(page);
374                         retval = 1;
375                 }
376                 write_unlock_irq(&swapper_space.tree_lock);
377         }
378         spin_unlock(&swap_lock);
379
380         if (retval) {
381                 swap_free(entry);
382                 page_cache_release(page);
383         }
384
385         return retval;
386 }
387
388 /*
389  * Free the swap entry like above, but also try to
390  * free the page cache entry if it is the last user.
391  */
392 void free_swap_and_cache(swp_entry_t entry)
393 {
394         struct swap_info_struct * p;
395         struct page *page = NULL;
396
397         if (is_migration_entry(entry))
398                 return;
399
400         p = swap_info_get(entry);
401         if (p) {
402                 if (swap_entry_free(p, swp_offset(entry)) == 1) {
403                         page = find_get_page(&swapper_space, entry.val);
404                         if (page && unlikely(TestSetPageLocked(page))) {
405                                 page_cache_release(page);
406                                 page = NULL;
407                         }
408                 }
409                 spin_unlock(&swap_lock);
410         }
411         if (page) {
412                 int one_user;
413
414                 BUG_ON(PagePrivate(page));
415                 one_user = (page_count(page) == 2);
416                 /* Only cache user (+us), or swap space full? Free it! */
417                 /* Also recheck PageSwapCache after page is locked (above) */
418                 if (PageSwapCache(page) && !PageWriteback(page) &&
419                                         (one_user || vm_swap_full())) {
420                         delete_from_swap_cache(page);
421                         SetPageDirty(page);
422                 }
423                 unlock_page(page);
424                 page_cache_release(page);
425         }
426 }
427
428 #ifdef CONFIG_HIBERNATION
429 /*
430  * Find the swap type that corresponds to given device (if any).
431  *
432  * @offset - number of the PAGE_SIZE-sized block of the device, starting
433  * from 0, in which the swap header is expected to be located.
434  *
435  * This is needed for the suspend to disk (aka swsusp).
436  */
437 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
438 {
439         struct block_device *bdev = NULL;
440         int i;
441
442         if (device)
443                 bdev = bdget(device);
444
445         spin_lock(&swap_lock);
446         for (i = 0; i < nr_swapfiles; i++) {
447                 struct swap_info_struct *sis = swap_info + i;
448
449                 if (!(sis->flags & SWP_WRITEOK))
450                         continue;
451
452                 if (!bdev) {
453                         if (bdev_p)
454                                 *bdev_p = sis->bdev;
455
456                         spin_unlock(&swap_lock);
457                         return i;
458                 }
459                 if (bdev == sis->bdev) {
460                         struct swap_extent *se;
461
462                         se = list_entry(sis->extent_list.next,
463                                         struct swap_extent, list);
464                         if (se->start_block == offset) {
465                                 if (bdev_p)
466                                         *bdev_p = sis->bdev;
467
468                                 spin_unlock(&swap_lock);
469                                 bdput(bdev);
470                                 return i;
471                         }
472                 }
473         }
474         spin_unlock(&swap_lock);
475         if (bdev)
476                 bdput(bdev);
477
478         return -ENODEV;
479 }
480
481 /*
482  * Return either the total number of swap pages of given type, or the number
483  * of free pages of that type (depending on @free)
484  *
485  * This is needed for software suspend
486  */
487 unsigned int count_swap_pages(int type, int free)
488 {
489         unsigned int n = 0;
490
491         if (type < nr_swapfiles) {
492                 spin_lock(&swap_lock);
493                 if (swap_info[type].flags & SWP_WRITEOK) {
494                         n = swap_info[type].pages;
495                         if (free)
496                                 n -= swap_info[type].inuse_pages;
497                 }
498                 spin_unlock(&swap_lock);
499         }
500         return n;
501 }
502 #endif
503
504 /*
505  * No need to decide whether this PTE shares the swap entry with others,
506  * just let do_wp_page work it out if a write is requested later - to
507  * force COW, vm_page_prot omits write permission from any private vma.
508  */
509 static void unuse_pte(struct vm_area_struct *vma, pte_t *pte,
510                 unsigned long addr, swp_entry_t entry, struct page *page)
511 {
512         inc_mm_counter(vma->vm_mm, anon_rss);
513         get_page(page);
514         set_pte_at(vma->vm_mm, addr, pte,
515                    pte_mkold(mk_pte(page, vma->vm_page_prot)));
516         page_add_anon_rmap(page, vma, addr);
517         swap_free(entry);
518         /*
519          * Move the page to the active list so it is not
520          * immediately swapped out again after swapon.
521          */
522         activate_page(page);
523 }
524
525 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
526                                 unsigned long addr, unsigned long end,
527                                 swp_entry_t entry, struct page *page)
528 {
529         pte_t swp_pte = swp_entry_to_pte(entry);
530         pte_t *pte;
531         spinlock_t *ptl;
532         int found = 0;
533
534         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
535         do {
536                 /*
537                  * swapoff spends a _lot_ of time in this loop!
538                  * Test inline before going to call unuse_pte.
539                  */
540                 if (unlikely(pte_same(*pte, swp_pte))) {
541                         unuse_pte(vma, pte++, addr, entry, page);
542                         found = 1;
543                         break;
544                 }
545         } while (pte++, addr += PAGE_SIZE, addr != end);
546         pte_unmap_unlock(pte - 1, ptl);
547         return found;
548 }
549
550 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
551                                 unsigned long addr, unsigned long end,
552                                 swp_entry_t entry, struct page *page)
553 {
554         pmd_t *pmd;
555         unsigned long next;
556
557         pmd = pmd_offset(pud, addr);
558         do {
559                 next = pmd_addr_end(addr, end);
560                 if (pmd_none_or_clear_bad(pmd))
561                         continue;
562                 if (unuse_pte_range(vma, pmd, addr, next, entry, page))
563                         return 1;
564         } while (pmd++, addr = next, addr != end);
565         return 0;
566 }
567
568 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
569                                 unsigned long addr, unsigned long end,
570                                 swp_entry_t entry, struct page *page)
571 {
572         pud_t *pud;
573         unsigned long next;
574
575         pud = pud_offset(pgd, addr);
576         do {
577                 next = pud_addr_end(addr, end);
578                 if (pud_none_or_clear_bad(pud))
579                         continue;
580                 if (unuse_pmd_range(vma, pud, addr, next, entry, page))
581                         return 1;
582         } while (pud++, addr = next, addr != end);
583         return 0;
584 }
585
586 static int unuse_vma(struct vm_area_struct *vma,
587                                 swp_entry_t entry, struct page *page)
588 {
589         pgd_t *pgd;
590         unsigned long addr, end, next;
591
592         if (page->mapping) {
593                 addr = page_address_in_vma(page, vma);
594                 if (addr == -EFAULT)
595                         return 0;
596                 else
597                         end = addr + PAGE_SIZE;
598         } else {
599                 addr = vma->vm_start;
600                 end = vma->vm_end;
601         }
602
603         pgd = pgd_offset(vma->vm_mm, addr);
604         do {
605                 next = pgd_addr_end(addr, end);
606                 if (pgd_none_or_clear_bad(pgd))
607                         continue;
608                 if (unuse_pud_range(vma, pgd, addr, next, entry, page))
609                         return 1;
610         } while (pgd++, addr = next, addr != end);
611         return 0;
612 }
613
614 static int unuse_mm(struct mm_struct *mm,
615                                 swp_entry_t entry, struct page *page)
616 {
617         struct vm_area_struct *vma;
618
619         if (!down_read_trylock(&mm->mmap_sem)) {
620                 /*
621                  * Activate page so shrink_cache is unlikely to unmap its
622                  * ptes while lock is dropped, so swapoff can make progress.
623                  */
624                 activate_page(page);
625                 unlock_page(page);
626                 down_read(&mm->mmap_sem);
627                 lock_page(page);
628         }
629         for (vma = mm->mmap; vma; vma = vma->vm_next) {
630                 if (vma->anon_vma && unuse_vma(vma, entry, page))
631                         break;
632         }
633         up_read(&mm->mmap_sem);
634         /*
635          * Currently unuse_mm cannot fail, but leave error handling
636          * at call sites for now, since we change it from time to time.
637          */
638         return 0;
639 }
640
641 /*
642  * Scan swap_map from current position to next entry still in use.
643  * Recycle to start on reaching the end, returning 0 when empty.
644  */
645 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
646                                         unsigned int prev)
647 {
648         unsigned int max = si->max;
649         unsigned int i = prev;
650         int count;
651
652         /*
653          * No need for swap_lock here: we're just looking
654          * for whether an entry is in use, not modifying it; false
655          * hits are okay, and sys_swapoff() has already prevented new
656          * allocations from this area (while holding swap_lock).
657          */
658         for (;;) {
659                 if (++i >= max) {
660                         if (!prev) {
661                                 i = 0;
662                                 break;
663                         }
664                         /*
665                          * No entries in use at top of swap_map,
666                          * loop back to start and recheck there.
667                          */
668                         max = prev + 1;
669                         prev = 0;
670                         i = 1;
671                 }
672                 count = si->swap_map[i];
673                 if (count && count != SWAP_MAP_BAD)
674                         break;
675         }
676         return i;
677 }
678
679 /*
680  * We completely avoid races by reading each swap page in advance,
681  * and then search for the process using it.  All the necessary
682  * page table adjustments can then be made atomically.
683  */
684 static int try_to_unuse(unsigned int type)
685 {
686         struct swap_info_struct * si = &swap_info[type];
687         struct mm_struct *start_mm;
688         unsigned short *swap_map;
689         unsigned short swcount;
690         struct page *page;
691         swp_entry_t entry;
692         unsigned int i = 0;
693         int retval = 0;
694         int reset_overflow = 0;
695         int shmem;
696
697         /*
698          * When searching mms for an entry, a good strategy is to
699          * start at the first mm we freed the previous entry from
700          * (though actually we don't notice whether we or coincidence
701          * freed the entry).  Initialize this start_mm with a hold.
702          *
703          * A simpler strategy would be to start at the last mm we
704          * freed the previous entry from; but that would take less
705          * advantage of mmlist ordering, which clusters forked mms
706          * together, child after parent.  If we race with dup_mmap(), we
707          * prefer to resolve parent before child, lest we miss entries
708          * duplicated after we scanned child: using last mm would invert
709          * that.  Though it's only a serious concern when an overflowed
710          * swap count is reset from SWAP_MAP_MAX, preventing a rescan.
711          */
712         start_mm = &init_mm;
713         atomic_inc(&init_mm.mm_users);
714
715         /*
716          * Keep on scanning until all entries have gone.  Usually,
717          * one pass through swap_map is enough, but not necessarily:
718          * there are races when an instance of an entry might be missed.
719          */
720         while ((i = find_next_to_unuse(si, i)) != 0) {
721                 if (signal_pending(current)) {
722                         retval = -EINTR;
723                         break;
724                 }
725
726                 /* 
727                  * Get a page for the entry, using the existing swap
728                  * cache page if there is one.  Otherwise, get a clean
729                  * page and read the swap into it. 
730                  */
731                 swap_map = &si->swap_map[i];
732                 entry = swp_entry(type, i);
733                 page = read_swap_cache_async(entry,
734                                         GFP_HIGHUSER_MOVABLE, NULL, 0);
735                 if (!page) {
736                         /*
737                          * Either swap_duplicate() failed because entry
738                          * has been freed independently, and will not be
739                          * reused since sys_swapoff() already disabled
740                          * allocation from here, or alloc_page() failed.
741                          */
742                         if (!*swap_map)
743                                 continue;
744                         retval = -ENOMEM;
745                         break;
746                 }
747
748                 /*
749                  * Don't hold on to start_mm if it looks like exiting.
750                  */
751                 if (atomic_read(&start_mm->mm_users) == 1) {
752                         mmput(start_mm);
753                         start_mm = &init_mm;
754                         atomic_inc(&init_mm.mm_users);
755                 }
756
757                 /*
758                  * Wait for and lock page.  When do_swap_page races with
759                  * try_to_unuse, do_swap_page can handle the fault much
760                  * faster than try_to_unuse can locate the entry.  This
761                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
762                  * defer to do_swap_page in such a case - in some tests,
763                  * do_swap_page and try_to_unuse repeatedly compete.
764                  */
765                 wait_on_page_locked(page);
766                 wait_on_page_writeback(page);
767                 lock_page(page);
768                 wait_on_page_writeback(page);
769
770                 /*
771                  * Remove all references to entry.
772                  * Whenever we reach init_mm, there's no address space
773                  * to search, but use it as a reminder to search shmem.
774                  */
775                 shmem = 0;
776                 swcount = *swap_map;
777                 if (swcount > 1) {
778                         if (start_mm == &init_mm)
779                                 shmem = shmem_unuse(entry, page);
780                         else
781                                 retval = unuse_mm(start_mm, entry, page);
782                 }
783                 if (*swap_map > 1) {
784                         int set_start_mm = (*swap_map >= swcount);
785                         struct list_head *p = &start_mm->mmlist;
786                         struct mm_struct *new_start_mm = start_mm;
787                         struct mm_struct *prev_mm = start_mm;
788                         struct mm_struct *mm;
789
790                         atomic_inc(&new_start_mm->mm_users);
791                         atomic_inc(&prev_mm->mm_users);
792                         spin_lock(&mmlist_lock);
793                         while (*swap_map > 1 && !retval &&
794                                         (p = p->next) != &start_mm->mmlist) {
795                                 mm = list_entry(p, struct mm_struct, mmlist);
796                                 if (!atomic_inc_not_zero(&mm->mm_users))
797                                         continue;
798                                 spin_unlock(&mmlist_lock);
799                                 mmput(prev_mm);
800                                 prev_mm = mm;
801
802                                 cond_resched();
803
804                                 swcount = *swap_map;
805                                 if (swcount <= 1)
806                                         ;
807                                 else if (mm == &init_mm) {
808                                         set_start_mm = 1;
809                                         shmem = shmem_unuse(entry, page);
810                                 } else
811                                         retval = unuse_mm(mm, entry, page);
812                                 if (set_start_mm && *swap_map < swcount) {
813                                         mmput(new_start_mm);
814                                         atomic_inc(&mm->mm_users);
815                                         new_start_mm = mm;
816                                         set_start_mm = 0;
817                                 }
818                                 spin_lock(&mmlist_lock);
819                         }
820                         spin_unlock(&mmlist_lock);
821                         mmput(prev_mm);
822                         mmput(start_mm);
823                         start_mm = new_start_mm;
824                 }
825                 if (retval) {
826                         unlock_page(page);
827                         page_cache_release(page);
828                         break;
829                 }
830
831                 /*
832                  * How could swap count reach 0x7fff when the maximum
833                  * pid is 0x7fff, and there's no way to repeat a swap
834                  * page within an mm (except in shmem, where it's the
835                  * shared object which takes the reference count)?
836                  * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
837                  *
838                  * If that's wrong, then we should worry more about
839                  * exit_mmap() and do_munmap() cases described above:
840                  * we might be resetting SWAP_MAP_MAX too early here.
841                  * We know "Undead"s can happen, they're okay, so don't
842                  * report them; but do report if we reset SWAP_MAP_MAX.
843                  */
844                 if (*swap_map == SWAP_MAP_MAX) {
845                         spin_lock(&swap_lock);
846                         *swap_map = 1;
847                         spin_unlock(&swap_lock);
848                         reset_overflow = 1;
849                 }
850
851                 /*
852                  * If a reference remains (rare), we would like to leave
853                  * the page in the swap cache; but try_to_unmap could
854                  * then re-duplicate the entry once we drop page lock,
855                  * so we might loop indefinitely; also, that page could
856                  * not be swapped out to other storage meanwhile.  So:
857                  * delete from cache even if there's another reference,
858                  * after ensuring that the data has been saved to disk -
859                  * since if the reference remains (rarer), it will be
860                  * read from disk into another page.  Splitting into two
861                  * pages would be incorrect if swap supported "shared
862                  * private" pages, but they are handled by tmpfs files.
863                  *
864                  * Note shmem_unuse already deleted a swappage from
865                  * the swap cache, unless the move to filepage failed:
866                  * in which case it left swappage in cache, lowered its
867                  * swap count to pass quickly through the loops above,
868                  * and now we must reincrement count to try again later.
869                  */
870                 if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
871                         struct writeback_control wbc = {
872                                 .sync_mode = WB_SYNC_NONE,
873                         };
874
875                         swap_writepage(page, &wbc);
876                         lock_page(page);
877                         wait_on_page_writeback(page);
878                 }
879                 if (PageSwapCache(page)) {
880                         if (shmem)
881                                 swap_duplicate(entry);
882                         else
883                                 delete_from_swap_cache(page);
884                 }
885
886                 /*
887                  * So we could skip searching mms once swap count went
888                  * to 1, we did not mark any present ptes as dirty: must
889                  * mark page dirty so shrink_page_list will preserve it.
890                  */
891                 SetPageDirty(page);
892                 unlock_page(page);
893                 page_cache_release(page);
894
895                 /*
896                  * Make sure that we aren't completely killing
897                  * interactive performance.
898                  */
899                 cond_resched();
900         }
901
902         mmput(start_mm);
903         if (reset_overflow) {
904                 printk(KERN_WARNING "swapoff: cleared swap entry overflow\n");
905                 swap_overflow = 0;
906         }
907         return retval;
908 }
909
910 /*
911  * After a successful try_to_unuse, if no swap is now in use, we know
912  * we can empty the mmlist.  swap_lock must be held on entry and exit.
913  * Note that mmlist_lock nests inside swap_lock, and an mm must be
914  * added to the mmlist just after page_duplicate - before would be racy.
915  */
916 static void drain_mmlist(void)
917 {
918         struct list_head *p, *next;
919         unsigned int i;
920
921         for (i = 0; i < nr_swapfiles; i++)
922                 if (swap_info[i].inuse_pages)
923                         return;
924         spin_lock(&mmlist_lock);
925         list_for_each_safe(p, next, &init_mm.mmlist)
926                 list_del_init(p);
927         spin_unlock(&mmlist_lock);
928 }
929
930 /*
931  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
932  * corresponds to page offset `offset'.
933  */
934 sector_t map_swap_page(struct swap_info_struct *sis, pgoff_t offset)
935 {
936         struct swap_extent *se = sis->curr_swap_extent;
937         struct swap_extent *start_se = se;
938
939         for ( ; ; ) {
940                 struct list_head *lh;
941
942                 if (se->start_page <= offset &&
943                                 offset < (se->start_page + se->nr_pages)) {
944                         return se->start_block + (offset - se->start_page);
945                 }
946                 lh = se->list.next;
947                 if (lh == &sis->extent_list)
948                         lh = lh->next;
949                 se = list_entry(lh, struct swap_extent, list);
950                 sis->curr_swap_extent = se;
951                 BUG_ON(se == start_se);         /* It *must* be present */
952         }
953 }
954
955 #ifdef CONFIG_HIBERNATION
956 /*
957  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
958  * corresponding to given index in swap_info (swap type).
959  */
960 sector_t swapdev_block(int swap_type, pgoff_t offset)
961 {
962         struct swap_info_struct *sis;
963
964         if (swap_type >= nr_swapfiles)
965                 return 0;
966
967         sis = swap_info + swap_type;
968         return (sis->flags & SWP_WRITEOK) ? map_swap_page(sis, offset) : 0;
969 }
970 #endif /* CONFIG_HIBERNATION */
971
972 /*
973  * Free all of a swapdev's extent information
974  */
975 static void destroy_swap_extents(struct swap_info_struct *sis)
976 {
977         while (!list_empty(&sis->extent_list)) {
978                 struct swap_extent *se;
979
980                 se = list_entry(sis->extent_list.next,
981                                 struct swap_extent, list);
982                 list_del(&se->list);
983                 kfree(se);
984         }
985 }
986
987 /*
988  * Add a block range (and the corresponding page range) into this swapdev's
989  * extent list.  The extent list is kept sorted in page order.
990  *
991  * This function rather assumes that it is called in ascending page order.
992  */
993 static int
994 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
995                 unsigned long nr_pages, sector_t start_block)
996 {
997         struct swap_extent *se;
998         struct swap_extent *new_se;
999         struct list_head *lh;
1000
1001         lh = sis->extent_list.prev;     /* The highest page extent */
1002         if (lh != &sis->extent_list) {
1003                 se = list_entry(lh, struct swap_extent, list);
1004                 BUG_ON(se->start_page + se->nr_pages != start_page);
1005                 if (se->start_block + se->nr_pages == start_block) {
1006                         /* Merge it */
1007                         se->nr_pages += nr_pages;
1008                         return 0;
1009                 }
1010         }
1011
1012         /*
1013          * No merge.  Insert a new extent, preserving ordering.
1014          */
1015         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1016         if (new_se == NULL)
1017                 return -ENOMEM;
1018         new_se->start_page = start_page;
1019         new_se->nr_pages = nr_pages;
1020         new_se->start_block = start_block;
1021
1022         list_add_tail(&new_se->list, &sis->extent_list);
1023         return 1;
1024 }
1025
1026 /*
1027  * A `swap extent' is a simple thing which maps a contiguous range of pages
1028  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1029  * is built at swapon time and is then used at swap_writepage/swap_readpage
1030  * time for locating where on disk a page belongs.
1031  *
1032  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1033  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1034  * swap files identically.
1035  *
1036  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1037  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1038  * swapfiles are handled *identically* after swapon time.
1039  *
1040  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1041  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1042  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1043  * requirements, they are simply tossed out - we will never use those blocks
1044  * for swapping.
1045  *
1046  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1047  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1048  * which will scribble on the fs.
1049  *
1050  * The amount of disk space which a single swap extent represents varies.
1051  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1052  * extents in the list.  To avoid much list walking, we cache the previous
1053  * search location in `curr_swap_extent', and start new searches from there.
1054  * This is extremely effective.  The average number of iterations in
1055  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1056  */
1057 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1058 {
1059         struct inode *inode;
1060         unsigned blocks_per_page;
1061         unsigned long page_no;
1062         unsigned blkbits;
1063         sector_t probe_block;
1064         sector_t last_block;
1065         sector_t lowest_block = -1;
1066         sector_t highest_block = 0;
1067         int nr_extents = 0;
1068         int ret;
1069
1070         inode = sis->swap_file->f_mapping->host;
1071         if (S_ISBLK(inode->i_mode)) {
1072                 ret = add_swap_extent(sis, 0, sis->max, 0);
1073                 *span = sis->pages;
1074                 goto done;
1075         }
1076
1077         blkbits = inode->i_blkbits;
1078         blocks_per_page = PAGE_SIZE >> blkbits;
1079
1080         /*
1081          * Map all the blocks into the extent list.  This code doesn't try
1082          * to be very smart.
1083          */
1084         probe_block = 0;
1085         page_no = 0;
1086         last_block = i_size_read(inode) >> blkbits;
1087         while ((probe_block + blocks_per_page) <= last_block &&
1088                         page_no < sis->max) {
1089                 unsigned block_in_page;
1090                 sector_t first_block;
1091
1092                 first_block = bmap(inode, probe_block);
1093                 if (first_block == 0)
1094                         goto bad_bmap;
1095
1096                 /*
1097                  * It must be PAGE_SIZE aligned on-disk
1098                  */
1099                 if (first_block & (blocks_per_page - 1)) {
1100                         probe_block++;
1101                         goto reprobe;
1102                 }
1103
1104                 for (block_in_page = 1; block_in_page < blocks_per_page;
1105                                         block_in_page++) {
1106                         sector_t block;
1107
1108                         block = bmap(inode, probe_block + block_in_page);
1109                         if (block == 0)
1110                                 goto bad_bmap;
1111                         if (block != first_block + block_in_page) {
1112                                 /* Discontiguity */
1113                                 probe_block++;
1114                                 goto reprobe;
1115                         }
1116                 }
1117
1118                 first_block >>= (PAGE_SHIFT - blkbits);
1119                 if (page_no) {  /* exclude the header page */
1120                         if (first_block < lowest_block)
1121                                 lowest_block = first_block;
1122                         if (first_block > highest_block)
1123                                 highest_block = first_block;
1124                 }
1125
1126                 /*
1127                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
1128                  */
1129                 ret = add_swap_extent(sis, page_no, 1, first_block);
1130                 if (ret < 0)
1131                         goto out;
1132                 nr_extents += ret;
1133                 page_no++;
1134                 probe_block += blocks_per_page;
1135 reprobe:
1136                 continue;
1137         }
1138         ret = nr_extents;
1139         *span = 1 + highest_block - lowest_block;
1140         if (page_no == 0)
1141                 page_no = 1;    /* force Empty message */
1142         sis->max = page_no;
1143         sis->pages = page_no - 1;
1144         sis->highest_bit = page_no - 1;
1145 done:
1146         sis->curr_swap_extent = list_entry(sis->extent_list.prev,
1147                                         struct swap_extent, list);
1148         goto out;
1149 bad_bmap:
1150         printk(KERN_ERR "swapon: swapfile has holes\n");
1151         ret = -EINVAL;
1152 out:
1153         return ret;
1154 }
1155
1156 #if 0   /* We don't need this yet */
1157 #include <linux/backing-dev.h>
1158 int page_queue_congested(struct page *page)
1159 {
1160         struct backing_dev_info *bdi;
1161
1162         BUG_ON(!PageLocked(page));      /* It pins the swap_info_struct */
1163
1164         if (PageSwapCache(page)) {
1165                 swp_entry_t entry = { .val = page_private(page) };
1166                 struct swap_info_struct *sis;
1167
1168                 sis = get_swap_info_struct(swp_type(entry));
1169                 bdi = sis->bdev->bd_inode->i_mapping->backing_dev_info;
1170         } else
1171                 bdi = page->mapping->backing_dev_info;
1172         return bdi_write_congested(bdi);
1173 }
1174 #endif
1175
1176 asmlinkage long sys_swapoff(const char __user * specialfile)
1177 {
1178         struct swap_info_struct * p = NULL;
1179         unsigned short *swap_map;
1180         struct file *swap_file, *victim;
1181         struct address_space *mapping;
1182         struct inode *inode;
1183         char * pathname;
1184         int i, type, prev;
1185         int err;
1186         
1187         if (!capable(CAP_SYS_ADMIN))
1188                 return -EPERM;
1189
1190         pathname = getname(specialfile);
1191         err = PTR_ERR(pathname);
1192         if (IS_ERR(pathname))
1193                 goto out;
1194
1195         victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
1196         putname(pathname);
1197         err = PTR_ERR(victim);
1198         if (IS_ERR(victim))
1199                 goto out;
1200
1201         mapping = victim->f_mapping;
1202         prev = -1;
1203         spin_lock(&swap_lock);
1204         for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
1205                 p = swap_info + type;
1206                 if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
1207                         if (p->swap_file->f_mapping == mapping)
1208                                 break;
1209                 }
1210                 prev = type;
1211         }
1212         if (type < 0) {
1213                 err = -EINVAL;
1214                 spin_unlock(&swap_lock);
1215                 goto out_dput;
1216         }
1217         if (!security_vm_enough_memory(p->pages))
1218                 vm_unacct_memory(p->pages);
1219         else {
1220                 err = -ENOMEM;
1221                 spin_unlock(&swap_lock);
1222                 goto out_dput;
1223         }
1224         if (prev < 0) {
1225                 swap_list.head = p->next;
1226         } else {
1227                 swap_info[prev].next = p->next;
1228         }
1229         if (type == swap_list.next) {
1230                 /* just pick something that's safe... */
1231                 swap_list.next = swap_list.head;
1232         }
1233         nr_swap_pages -= p->pages;
1234         total_swap_pages -= p->pages;
1235         p->flags &= ~SWP_WRITEOK;
1236         spin_unlock(&swap_lock);
1237
1238         current->flags |= PF_SWAPOFF;
1239         err = try_to_unuse(type);
1240         current->flags &= ~PF_SWAPOFF;
1241
1242         if (err) {
1243                 /* re-insert swap space back into swap_list */
1244                 spin_lock(&swap_lock);
1245                 for (prev = -1, i = swap_list.head; i >= 0; prev = i, i = swap_info[i].next)
1246                         if (p->prio >= swap_info[i].prio)
1247                                 break;
1248                 p->next = i;
1249                 if (prev < 0)
1250                         swap_list.head = swap_list.next = p - swap_info;
1251                 else
1252                         swap_info[prev].next = p - swap_info;
1253                 nr_swap_pages += p->pages;
1254                 total_swap_pages += p->pages;
1255                 p->flags |= SWP_WRITEOK;
1256                 spin_unlock(&swap_lock);
1257                 goto out_dput;
1258         }
1259
1260         /* wait for any unplug function to finish */
1261         down_write(&swap_unplug_sem);
1262         up_write(&swap_unplug_sem);
1263
1264         destroy_swap_extents(p);
1265         mutex_lock(&swapon_mutex);
1266         spin_lock(&swap_lock);
1267         drain_mmlist();
1268
1269         /* wait for anyone still in scan_swap_map */
1270         p->highest_bit = 0;             /* cuts scans short */
1271         while (p->flags >= SWP_SCANNING) {
1272                 spin_unlock(&swap_lock);
1273                 schedule_timeout_uninterruptible(1);
1274                 spin_lock(&swap_lock);
1275         }
1276
1277         swap_file = p->swap_file;
1278         p->swap_file = NULL;
1279         p->max = 0;
1280         swap_map = p->swap_map;
1281         p->swap_map = NULL;
1282         p->flags = 0;
1283         spin_unlock(&swap_lock);
1284         mutex_unlock(&swapon_mutex);
1285         vfree(swap_map);
1286         inode = mapping->host;
1287         if (S_ISBLK(inode->i_mode)) {
1288                 struct block_device *bdev = I_BDEV(inode);
1289                 set_blocksize(bdev, p->old_block_size);
1290                 bd_release(bdev);
1291         } else {
1292                 mutex_lock(&inode->i_mutex);
1293                 inode->i_flags &= ~S_SWAPFILE;
1294                 mutex_unlock(&inode->i_mutex);
1295         }
1296         filp_close(swap_file, NULL);
1297         err = 0;
1298
1299 out_dput:
1300         filp_close(victim, NULL);
1301 out:
1302         return err;
1303 }
1304
1305 #ifdef CONFIG_PROC_FS
1306 /* iterator */
1307 static void *swap_start(struct seq_file *swap, loff_t *pos)
1308 {
1309         struct swap_info_struct *ptr = swap_info;
1310         int i;
1311         loff_t l = *pos;
1312
1313         mutex_lock(&swapon_mutex);
1314
1315         if (!l)
1316                 return SEQ_START_TOKEN;
1317
1318         for (i = 0; i < nr_swapfiles; i++, ptr++) {
1319                 if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
1320                         continue;
1321                 if (!--l)
1322                         return ptr;
1323         }
1324
1325         return NULL;
1326 }
1327
1328 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1329 {
1330         struct swap_info_struct *ptr;
1331         struct swap_info_struct *endptr = swap_info + nr_swapfiles;
1332
1333         if (v == SEQ_START_TOKEN)
1334                 ptr = swap_info;
1335         else {
1336                 ptr = v;
1337                 ptr++;
1338         }
1339
1340         for (; ptr < endptr; ptr++) {
1341                 if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
1342                         continue;
1343                 ++*pos;
1344                 return ptr;
1345         }
1346
1347         return NULL;
1348 }
1349
1350 static void swap_stop(struct seq_file *swap, void *v)
1351 {
1352         mutex_unlock(&swapon_mutex);
1353 }
1354
1355 static int swap_show(struct seq_file *swap, void *v)
1356 {
1357         struct swap_info_struct *ptr = v;
1358         struct file *file;
1359         int len;
1360
1361         if (ptr == SEQ_START_TOKEN) {
1362                 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1363                 return 0;
1364         }
1365
1366         file = ptr->swap_file;
1367         len = seq_path(swap, file->f_path.mnt, file->f_path.dentry, " \t\n\\");
1368         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1369                        len < 40 ? 40 - len : 1, " ",
1370                        S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
1371                                 "partition" : "file\t",
1372                        ptr->pages << (PAGE_SHIFT - 10),
1373                        ptr->inuse_pages << (PAGE_SHIFT - 10),
1374                        ptr->prio);
1375         return 0;
1376 }
1377
1378 static const struct seq_operations swaps_op = {
1379         .start =        swap_start,
1380         .next =         swap_next,
1381         .stop =         swap_stop,
1382         .show =         swap_show
1383 };
1384
1385 static int swaps_open(struct inode *inode, struct file *file)
1386 {
1387         return seq_open(file, &swaps_op);
1388 }
1389
1390 static const struct file_operations proc_swaps_operations = {
1391         .open           = swaps_open,
1392         .read           = seq_read,
1393         .llseek         = seq_lseek,
1394         .release        = seq_release,
1395 };
1396
1397 static int __init procswaps_init(void)
1398 {
1399         struct proc_dir_entry *entry;
1400
1401         entry = create_proc_entry("swaps", 0, NULL);
1402         if (entry)
1403                 entry->proc_fops = &proc_swaps_operations;
1404         return 0;
1405 }
1406 __initcall(procswaps_init);
1407 #endif /* CONFIG_PROC_FS */
1408
1409 /*
1410  * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
1411  *
1412  * The swapon system call
1413  */
1414 asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
1415 {
1416         struct swap_info_struct * p;
1417         char *name = NULL;
1418         struct block_device *bdev = NULL;
1419         struct file *swap_file = NULL;
1420         struct address_space *mapping;
1421         unsigned int type;
1422         int i, prev;
1423         int error;
1424         static int least_priority;
1425         union swap_header *swap_header = NULL;
1426         int swap_header_version;
1427         unsigned int nr_good_pages = 0;
1428         int nr_extents = 0;
1429         sector_t span;
1430         unsigned long maxpages = 1;
1431         int swapfilesize;
1432         unsigned short *swap_map;
1433         struct page *page = NULL;
1434         struct inode *inode = NULL;
1435         int did_down = 0;
1436
1437         if (!capable(CAP_SYS_ADMIN))
1438                 return -EPERM;
1439         spin_lock(&swap_lock);
1440         p = swap_info;
1441         for (type = 0 ; type < nr_swapfiles ; type++,p++)
1442                 if (!(p->flags & SWP_USED))
1443                         break;
1444         error = -EPERM;
1445         if (type >= MAX_SWAPFILES) {
1446                 spin_unlock(&swap_lock);
1447                 goto out;
1448         }
1449         if (type >= nr_swapfiles)
1450                 nr_swapfiles = type+1;
1451         INIT_LIST_HEAD(&p->extent_list);
1452         p->flags = SWP_USED;
1453         p->swap_file = NULL;
1454         p->old_block_size = 0;
1455         p->swap_map = NULL;
1456         p->lowest_bit = 0;
1457         p->highest_bit = 0;
1458         p->cluster_nr = 0;
1459         p->inuse_pages = 0;
1460         p->next = -1;
1461         if (swap_flags & SWAP_FLAG_PREFER) {
1462                 p->prio =
1463                   (swap_flags & SWAP_FLAG_PRIO_MASK)>>SWAP_FLAG_PRIO_SHIFT;
1464         } else {
1465                 p->prio = --least_priority;
1466         }
1467         spin_unlock(&swap_lock);
1468         name = getname(specialfile);
1469         error = PTR_ERR(name);
1470         if (IS_ERR(name)) {
1471                 name = NULL;
1472                 goto bad_swap_2;
1473         }
1474         swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
1475         error = PTR_ERR(swap_file);
1476         if (IS_ERR(swap_file)) {
1477                 swap_file = NULL;
1478                 goto bad_swap_2;
1479         }
1480
1481         p->swap_file = swap_file;
1482         mapping = swap_file->f_mapping;
1483         inode = mapping->host;
1484
1485         error = -EBUSY;
1486         for (i = 0; i < nr_swapfiles; i++) {
1487                 struct swap_info_struct *q = &swap_info[i];
1488
1489                 if (i == type || !q->swap_file)
1490                         continue;
1491                 if (mapping == q->swap_file->f_mapping)
1492                         goto bad_swap;
1493         }
1494
1495         error = -EINVAL;
1496         if (S_ISBLK(inode->i_mode)) {
1497                 bdev = I_BDEV(inode);
1498                 error = bd_claim(bdev, sys_swapon);
1499                 if (error < 0) {
1500                         bdev = NULL;
1501                         error = -EINVAL;
1502                         goto bad_swap;
1503                 }
1504                 p->old_block_size = block_size(bdev);
1505                 error = set_blocksize(bdev, PAGE_SIZE);
1506                 if (error < 0)
1507                         goto bad_swap;
1508                 p->bdev = bdev;
1509         } else if (S_ISREG(inode->i_mode)) {
1510                 p->bdev = inode->i_sb->s_bdev;
1511                 mutex_lock(&inode->i_mutex);
1512                 did_down = 1;
1513                 if (IS_SWAPFILE(inode)) {
1514                         error = -EBUSY;
1515                         goto bad_swap;
1516                 }
1517         } else {
1518                 goto bad_swap;
1519         }
1520
1521         swapfilesize = i_size_read(inode) >> PAGE_SHIFT;
1522
1523         /*
1524          * Read the swap header.
1525          */
1526         if (!mapping->a_ops->readpage) {
1527                 error = -EINVAL;
1528                 goto bad_swap;
1529         }
1530         page = read_mapping_page(mapping, 0, swap_file);
1531         if (IS_ERR(page)) {
1532                 error = PTR_ERR(page);
1533                 goto bad_swap;
1534         }
1535         kmap(page);
1536         swap_header = page_address(page);
1537
1538         if (!memcmp("SWAP-SPACE",swap_header->magic.magic,10))
1539                 swap_header_version = 1;
1540         else if (!memcmp("SWAPSPACE2",swap_header->magic.magic,10))
1541                 swap_header_version = 2;
1542         else {
1543                 printk(KERN_ERR "Unable to find swap-space signature\n");
1544                 error = -EINVAL;
1545                 goto bad_swap;
1546         }
1547         
1548         switch (swap_header_version) {
1549         case 1:
1550                 printk(KERN_ERR "version 0 swap is no longer supported. "
1551                         "Use mkswap -v1 %s\n", name);
1552                 error = -EINVAL;
1553                 goto bad_swap;
1554         case 2:
1555                 /* Check the swap header's sub-version and the size of
1556                    the swap file and bad block lists */
1557                 if (swap_header->info.version != 1) {
1558                         printk(KERN_WARNING
1559                                "Unable to handle swap header version %d\n",
1560                                swap_header->info.version);
1561                         error = -EINVAL;
1562                         goto bad_swap;
1563                 }
1564
1565                 p->lowest_bit  = 1;
1566                 p->cluster_next = 1;
1567
1568                 /*
1569                  * Find out how many pages are allowed for a single swap
1570                  * device. There are two limiting factors: 1) the number of
1571                  * bits for the swap offset in the swp_entry_t type and
1572                  * 2) the number of bits in the a swap pte as defined by
1573                  * the different architectures. In order to find the
1574                  * largest possible bit mask a swap entry with swap type 0
1575                  * and swap offset ~0UL is created, encoded to a swap pte,
1576                  * decoded to a swp_entry_t again and finally the swap
1577                  * offset is extracted. This will mask all the bits from
1578                  * the initial ~0UL mask that can't be encoded in either
1579                  * the swp_entry_t or the architecture definition of a
1580                  * swap pte.
1581                  */
1582                 maxpages = swp_offset(pte_to_swp_entry(swp_entry_to_pte(swp_entry(0,~0UL)))) - 1;
1583                 if (maxpages > swap_header->info.last_page)
1584                         maxpages = swap_header->info.last_page;
1585                 p->highest_bit = maxpages - 1;
1586
1587                 error = -EINVAL;
1588                 if (!maxpages)
1589                         goto bad_swap;
1590                 if (swapfilesize && maxpages > swapfilesize) {
1591                         printk(KERN_WARNING
1592                                "Swap area shorter than signature indicates\n");
1593                         goto bad_swap;
1594                 }
1595                 if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1596                         goto bad_swap;
1597                 if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1598                         goto bad_swap;
1599
1600                 /* OK, set up the swap map and apply the bad block list */
1601                 if (!(p->swap_map = vmalloc(maxpages * sizeof(short)))) {
1602                         error = -ENOMEM;
1603                         goto bad_swap;
1604                 }
1605
1606                 error = 0;
1607                 memset(p->swap_map, 0, maxpages * sizeof(short));
1608                 for (i = 0; i < swap_header->info.nr_badpages; i++) {
1609                         int page_nr = swap_header->info.badpages[i];
1610                         if (page_nr <= 0 || page_nr >= swap_header->info.last_page)
1611                                 error = -EINVAL;
1612                         else
1613                                 p->swap_map[page_nr] = SWAP_MAP_BAD;
1614                 }
1615                 nr_good_pages = swap_header->info.last_page -
1616                                 swap_header->info.nr_badpages -
1617                                 1 /* header page */;
1618                 if (error)
1619                         goto bad_swap;
1620         }
1621
1622         if (nr_good_pages) {
1623                 p->swap_map[0] = SWAP_MAP_BAD;
1624                 p->max = maxpages;
1625                 p->pages = nr_good_pages;
1626                 nr_extents = setup_swap_extents(p, &span);
1627                 if (nr_extents < 0) {
1628                         error = nr_extents;
1629                         goto bad_swap;
1630                 }
1631                 nr_good_pages = p->pages;
1632         }
1633         if (!nr_good_pages) {
1634                 printk(KERN_WARNING "Empty swap-file\n");
1635                 error = -EINVAL;
1636                 goto bad_swap;
1637         }
1638
1639         mutex_lock(&swapon_mutex);
1640         spin_lock(&swap_lock);
1641         p->flags = SWP_ACTIVE;
1642         nr_swap_pages += nr_good_pages;
1643         total_swap_pages += nr_good_pages;
1644
1645         printk(KERN_INFO "Adding %uk swap on %s.  "
1646                         "Priority:%d extents:%d across:%lluk\n",
1647                 nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
1648                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10));
1649
1650         /* insert swap space into swap_list: */
1651         prev = -1;
1652         for (i = swap_list.head; i >= 0; i = swap_info[i].next) {
1653                 if (p->prio >= swap_info[i].prio) {
1654                         break;
1655                 }
1656                 prev = i;
1657         }
1658         p->next = i;
1659         if (prev < 0) {
1660                 swap_list.head = swap_list.next = p - swap_info;
1661         } else {
1662                 swap_info[prev].next = p - swap_info;
1663         }
1664         spin_unlock(&swap_lock);
1665         mutex_unlock(&swapon_mutex);
1666         error = 0;
1667         goto out;
1668 bad_swap:
1669         if (bdev) {
1670                 set_blocksize(bdev, p->old_block_size);
1671                 bd_release(bdev);
1672         }
1673         destroy_swap_extents(p);
1674 bad_swap_2:
1675         spin_lock(&swap_lock);
1676         swap_map = p->swap_map;
1677         p->swap_file = NULL;
1678         p->swap_map = NULL;
1679         p->flags = 0;
1680         if (!(swap_flags & SWAP_FLAG_PREFER))
1681                 ++least_priority;
1682         spin_unlock(&swap_lock);
1683         vfree(swap_map);
1684         if (swap_file)
1685                 filp_close(swap_file, NULL);
1686 out:
1687         if (page && !IS_ERR(page)) {
1688                 kunmap(page);
1689                 page_cache_release(page);
1690         }
1691         if (name)
1692                 putname(name);
1693         if (did_down) {
1694                 if (!error)
1695                         inode->i_flags |= S_SWAPFILE;
1696                 mutex_unlock(&inode->i_mutex);
1697         }
1698         return error;
1699 }
1700
1701 void si_swapinfo(struct sysinfo *val)
1702 {
1703         unsigned int i;
1704         unsigned long nr_to_be_unused = 0;
1705
1706         spin_lock(&swap_lock);
1707         for (i = 0; i < nr_swapfiles; i++) {
1708                 if (!(swap_info[i].flags & SWP_USED) ||
1709                      (swap_info[i].flags & SWP_WRITEOK))
1710                         continue;
1711                 nr_to_be_unused += swap_info[i].inuse_pages;
1712         }
1713         val->freeswap = nr_swap_pages + nr_to_be_unused;
1714         val->totalswap = total_swap_pages + nr_to_be_unused;
1715         spin_unlock(&swap_lock);
1716 }
1717
1718 /*
1719  * Verify that a swap entry is valid and increment its swap map count.
1720  *
1721  * Note: if swap_map[] reaches SWAP_MAP_MAX the entries are treated as
1722  * "permanent", but will be reclaimed by the next swapoff.
1723  */
1724 int swap_duplicate(swp_entry_t entry)
1725 {
1726         struct swap_info_struct * p;
1727         unsigned long offset, type;
1728         int result = 0;
1729
1730         if (is_migration_entry(entry))
1731                 return 1;
1732
1733         type = swp_type(entry);
1734         if (type >= nr_swapfiles)
1735                 goto bad_file;
1736         p = type + swap_info;
1737         offset = swp_offset(entry);
1738
1739         spin_lock(&swap_lock);
1740         if (offset < p->max && p->swap_map[offset]) {
1741                 if (p->swap_map[offset] < SWAP_MAP_MAX - 1) {
1742                         p->swap_map[offset]++;
1743                         result = 1;
1744                 } else if (p->swap_map[offset] <= SWAP_MAP_MAX) {
1745                         if (swap_overflow++ < 5)
1746                                 printk(KERN_WARNING "swap_dup: swap entry overflow\n");
1747                         p->swap_map[offset] = SWAP_MAP_MAX;
1748                         result = 1;
1749                 }
1750         }
1751         spin_unlock(&swap_lock);
1752 out:
1753         return result;
1754
1755 bad_file:
1756         printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
1757         goto out;
1758 }
1759
1760 struct swap_info_struct *
1761 get_swap_info_struct(unsigned type)
1762 {
1763         return &swap_info[type];
1764 }
1765
1766 /*
1767  * swap_lock prevents swap_map being freed. Don't grab an extra
1768  * reference on the swaphandle, it doesn't matter if it becomes unused.
1769  */
1770 int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
1771 {
1772         int our_page_cluster = page_cluster;
1773         int ret = 0, i = 1 << our_page_cluster;
1774         unsigned long toff;
1775         struct swap_info_struct *swapdev = swp_type(entry) + swap_info;
1776
1777         if (!our_page_cluster)  /* no readahead */
1778                 return 0;
1779         toff = (swp_offset(entry) >> our_page_cluster) << our_page_cluster;
1780         if (!toff)              /* first page is swap header */
1781                 toff++, i--;
1782         *offset = toff;
1783
1784         spin_lock(&swap_lock);
1785         do {
1786                 /* Don't read-ahead past the end of the swap area */
1787                 if (toff >= swapdev->max)
1788                         break;
1789                 /* Don't read in free or bad pages */
1790                 if (!swapdev->swap_map[toff])
1791                         break;
1792                 if (swapdev->swap_map[toff] == SWAP_MAP_BAD)
1793                         break;
1794                 toff++;
1795                 ret++;
1796         } while (--i);
1797         spin_unlock(&swap_lock);
1798         return ret;
1799 }