1 // SPDX-License-Identifier: GPL-2.0
3 * linux/mm/swap_state.c
5 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
6 * Swap reorganised 29.12.95, Stephen Tweedie
8 * Rewritten to use page cache, (C) 1998 Stephen Tweedie
11 #include <linux/gfp.h>
12 #include <linux/kernel_stat.h>
13 #include <linux/swap.h>
14 #include <linux/swapops.h>
15 #include <linux/init.h>
16 #include <linux/pagemap.h>
17 #include <linux/backing-dev.h>
18 #include <linux/blkdev.h>
19 #include <linux/pagevec.h>
20 #include <linux/migrate.h>
21 #include <linux/vmalloc.h>
22 #include <linux/swap_slots.h>
23 #include <linux/huge_mm.h>
25 #include <asm/pgtable.h>
28 * swapper_space is a fiction, retained to simplify the path through
29 * vmscan's shrink_page_list.
31 static const struct address_space_operations swap_aops
= {
32 .writepage
= swap_writepage
,
33 .set_page_dirty
= swap_set_page_dirty
,
34 #ifdef CONFIG_MIGRATION
35 .migratepage
= migrate_page
,
39 struct address_space
*swapper_spaces
[MAX_SWAPFILES
] __read_mostly
;
40 static unsigned int nr_swapper_spaces
[MAX_SWAPFILES
] __read_mostly
;
41 static bool enable_vma_readahead __read_mostly
= true;
43 #define SWAP_RA_WIN_SHIFT (PAGE_SHIFT / 2)
44 #define SWAP_RA_HITS_MASK ((1UL << SWAP_RA_WIN_SHIFT) - 1)
45 #define SWAP_RA_HITS_MAX SWAP_RA_HITS_MASK
46 #define SWAP_RA_WIN_MASK (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
48 #define SWAP_RA_HITS(v) ((v) & SWAP_RA_HITS_MASK)
49 #define SWAP_RA_WIN(v) (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
50 #define SWAP_RA_ADDR(v) ((v) & PAGE_MASK)
52 #define SWAP_RA_VAL(addr, win, hits) \
53 (((addr) & PAGE_MASK) | \
54 (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) | \
55 ((hits) & SWAP_RA_HITS_MASK))
57 /* Initial readahead hits is 4 to start up with a small window */
58 #define GET_SWAP_RA_VAL(vma) \
59 (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
61 #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
62 #define ADD_CACHE_INFO(x, nr) do { swap_cache_info.x += (nr); } while (0)
65 unsigned long add_total
;
66 unsigned long del_total
;
67 unsigned long find_success
;
68 unsigned long find_total
;
71 unsigned long total_swapcache_pages(void)
73 unsigned int i
, j
, nr
;
74 unsigned long ret
= 0;
75 struct address_space
*spaces
;
78 for (i
= 0; i
< MAX_SWAPFILES
; i
++) {
80 * The corresponding entries in nr_swapper_spaces and
81 * swapper_spaces will be reused only after at least
82 * one grace period. So it is impossible for them
83 * belongs to different usage.
85 nr
= nr_swapper_spaces
[i
];
86 spaces
= rcu_dereference(swapper_spaces
[i
]);
89 for (j
= 0; j
< nr
; j
++)
90 ret
+= spaces
[j
].nrpages
;
96 static atomic_t swapin_readahead_hits
= ATOMIC_INIT(4);
98 void show_swap_cache_info(void)
100 printk("%lu pages in swap cache\n", total_swapcache_pages());
101 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
102 swap_cache_info
.add_total
, swap_cache_info
.del_total
,
103 swap_cache_info
.find_success
, swap_cache_info
.find_total
);
104 printk("Free swap = %ldkB\n",
105 get_nr_swap_pages() << (PAGE_SHIFT
- 10));
106 printk("Total swap = %lukB\n", total_swap_pages
<< (PAGE_SHIFT
- 10));
110 * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
111 * but sets SwapCache flag and private instead of mapping and index.
113 int add_to_swap_cache(struct page
*page
, swp_entry_t entry
, gfp_t gfp
)
115 struct address_space
*address_space
= swap_address_space(entry
);
116 pgoff_t idx
= swp_offset(entry
);
117 XA_STATE_ORDER(xas
, &address_space
->i_pages
, idx
, compound_order(page
));
118 unsigned long i
, nr
= 1UL << compound_order(page
);
120 VM_BUG_ON_PAGE(!PageLocked(page
), page
);
121 VM_BUG_ON_PAGE(PageSwapCache(page
), page
);
122 VM_BUG_ON_PAGE(!PageSwapBacked(page
), page
);
124 page_ref_add(page
, nr
);
125 SetPageSwapCache(page
);
129 xas_create_range(&xas
);
132 for (i
= 0; i
< nr
; i
++) {
133 VM_BUG_ON_PAGE(xas
.xa_index
!= idx
+ i
, page
);
134 set_page_private(page
+ i
, entry
.val
+ i
);
135 xas_store(&xas
, page
+ i
);
138 address_space
->nrpages
+= nr
;
139 __mod_node_page_state(page_pgdat(page
), NR_FILE_PAGES
, nr
);
140 ADD_CACHE_INFO(add_total
, nr
);
142 xas_unlock_irq(&xas
);
143 } while (xas_nomem(&xas
, gfp
));
145 if (!xas_error(&xas
))
148 ClearPageSwapCache(page
);
149 page_ref_sub(page
, nr
);
150 return xas_error(&xas
);
154 * This must be called only on pages that have
155 * been verified to be in the swap cache.
157 void __delete_from_swap_cache(struct page
*page
)
159 struct address_space
*address_space
;
160 int i
, nr
= hpage_nr_pages(page
);
164 VM_BUG_ON_PAGE(!PageLocked(page
), page
);
165 VM_BUG_ON_PAGE(!PageSwapCache(page
), page
);
166 VM_BUG_ON_PAGE(PageWriteback(page
), page
);
168 entry
.val
= page_private(page
);
169 address_space
= swap_address_space(entry
);
170 idx
= swp_offset(entry
);
171 for (i
= 0; i
< nr
; i
++) {
172 radix_tree_delete(&address_space
->i_pages
, idx
+ i
);
173 set_page_private(page
+ i
, 0);
175 ClearPageSwapCache(page
);
176 address_space
->nrpages
-= nr
;
177 __mod_node_page_state(page_pgdat(page
), NR_FILE_PAGES
, -nr
);
178 ADD_CACHE_INFO(del_total
, nr
);
182 * add_to_swap - allocate swap space for a page
183 * @page: page we want to move to swap
185 * Allocate swap space for the page and add the page to the
186 * swap cache. Caller needs to hold the page lock.
188 int add_to_swap(struct page
*page
)
193 VM_BUG_ON_PAGE(!PageLocked(page
), page
);
194 VM_BUG_ON_PAGE(!PageUptodate(page
), page
);
196 entry
= get_swap_page(page
);
201 * XArray node allocations from PF_MEMALLOC contexts could
202 * completely exhaust the page allocator. __GFP_NOMEMALLOC
203 * stops emergency reserves from being allocated.
205 * TODO: this could cause a theoretical memory reclaim
206 * deadlock in the swap out path.
209 * Add it to the swap cache.
211 err
= add_to_swap_cache(page
, entry
,
212 __GFP_HIGH
|__GFP_NOMEMALLOC
|__GFP_NOWARN
);
215 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
216 * clear SWAP_HAS_CACHE flag.
220 * Normally the page will be dirtied in unmap because its pte should be
221 * dirty. A special case is MADV_FREE page. The page'e pte could have
222 * dirty bit cleared but the page's SwapBacked bit is still set because
223 * clearing the dirty bit and SwapBacked bit has no lock protected. For
224 * such page, unmap will not set dirty bit for it, so page reclaim will
225 * not write the page out. This can cause data corruption when the page
226 * is swap in later. Always setting the dirty bit for the page solves
229 set_page_dirty(page
);
234 put_swap_page(page
, entry
);
239 * This must be called only on pages that have
240 * been verified to be in the swap cache and locked.
241 * It will never put the page into the free list,
242 * the caller has a reference on the page.
244 void delete_from_swap_cache(struct page
*page
)
247 struct address_space
*address_space
;
249 entry
.val
= page_private(page
);
251 address_space
= swap_address_space(entry
);
252 xa_lock_irq(&address_space
->i_pages
);
253 __delete_from_swap_cache(page
);
254 xa_unlock_irq(&address_space
->i_pages
);
256 put_swap_page(page
, entry
);
257 page_ref_sub(page
, hpage_nr_pages(page
));
261 * If we are the only user, then try to free up the swap cache.
263 * Its ok to check for PageSwapCache without the page lock
264 * here because we are going to recheck again inside
265 * try_to_free_swap() _with_ the lock.
268 static inline void free_swap_cache(struct page
*page
)
270 if (PageSwapCache(page
) && !page_mapped(page
) && trylock_page(page
)) {
271 try_to_free_swap(page
);
277 * Perform a free_page(), also freeing any swap cache associated with
278 * this page if it is the last user of the page.
280 void free_page_and_swap_cache(struct page
*page
)
282 free_swap_cache(page
);
283 if (!is_huge_zero_page(page
))
288 * Passed an array of pages, drop them all from swapcache and then release
289 * them. They are removed from the LRU and freed if this is their last use.
291 void free_pages_and_swap_cache(struct page
**pages
, int nr
)
293 struct page
**pagep
= pages
;
297 for (i
= 0; i
< nr
; i
++)
298 free_swap_cache(pagep
[i
]);
299 release_pages(pagep
, nr
);
302 static inline bool swap_use_vma_readahead(void)
304 return READ_ONCE(enable_vma_readahead
) && !atomic_read(&nr_rotate_swap
);
308 * Lookup a swap entry in the swap cache. A found page will be returned
309 * unlocked and with its refcount incremented - we rely on the kernel
310 * lock getting page table operations atomic even if we drop the page
311 * lock before returning.
313 struct page
*lookup_swap_cache(swp_entry_t entry
, struct vm_area_struct
*vma
,
318 page
= find_get_page(swap_address_space(entry
), swp_offset(entry
));
320 INC_CACHE_INFO(find_total
);
322 bool vma_ra
= swap_use_vma_readahead();
325 INC_CACHE_INFO(find_success
);
327 * At the moment, we don't support PG_readahead for anon THP
328 * so let's bail out rather than confusing the readahead stat.
330 if (unlikely(PageTransCompound(page
)))
333 readahead
= TestClearPageReadahead(page
);
335 unsigned long ra_val
;
338 ra_val
= GET_SWAP_RA_VAL(vma
);
339 win
= SWAP_RA_WIN(ra_val
);
340 hits
= SWAP_RA_HITS(ra_val
);
342 hits
= min_t(int, hits
+ 1, SWAP_RA_HITS_MAX
);
343 atomic_long_set(&vma
->swap_readahead_info
,
344 SWAP_RA_VAL(addr
, win
, hits
));
348 count_vm_event(SWAP_RA_HIT
);
350 atomic_inc(&swapin_readahead_hits
);
357 struct page
*__read_swap_cache_async(swp_entry_t entry
, gfp_t gfp_mask
,
358 struct vm_area_struct
*vma
, unsigned long addr
,
359 bool *new_page_allocated
)
361 struct page
*found_page
, *new_page
= NULL
;
362 struct address_space
*swapper_space
= swap_address_space(entry
);
364 *new_page_allocated
= false;
368 * First check the swap cache. Since this is normally
369 * called after lookup_swap_cache() failed, re-calling
370 * that would confuse statistics.
372 found_page
= find_get_page(swapper_space
, swp_offset(entry
));
377 * Just skip read ahead for unused swap slot.
378 * During swap_off when swap_slot_cache is disabled,
379 * we have to handle the race between putting
380 * swap entry in swap cache and marking swap slot
381 * as SWAP_HAS_CACHE. That's done in later part of code or
382 * else swap_off will be aborted if we return NULL.
384 if (!__swp_swapcount(entry
) && swap_slot_cache_enabled
)
388 * Get a new page to read into from swap.
391 new_page
= alloc_page_vma(gfp_mask
, vma
, addr
);
393 break; /* Out of memory */
397 * Swap entry may have been freed since our caller observed it.
399 err
= swapcache_prepare(entry
);
400 if (err
== -EEXIST
) {
402 * We might race against get_swap_page() and stumble
403 * across a SWAP_HAS_CACHE swap_map entry whose page
404 * has not been brought into the swapcache yet.
408 } else if (err
) /* swp entry is obsolete ? */
411 /* May fail (-ENOMEM) if XArray node allocation failed. */
412 __SetPageLocked(new_page
);
413 __SetPageSwapBacked(new_page
);
414 err
= add_to_swap_cache(new_page
, entry
, gfp_mask
& GFP_KERNEL
);
416 /* Initiate read into locked page */
417 lru_cache_add_anon(new_page
);
418 *new_page_allocated
= true;
421 __ClearPageLocked(new_page
);
423 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
424 * clear SWAP_HAS_CACHE flag.
426 put_swap_page(new_page
, entry
);
427 } while (err
!= -ENOMEM
);
435 * Locate a page of swap in physical memory, reserving swap cache space
436 * and reading the disk if it is not already cached.
437 * A failure return means that either the page allocation failed or that
438 * the swap entry is no longer in use.
440 struct page
*read_swap_cache_async(swp_entry_t entry
, gfp_t gfp_mask
,
441 struct vm_area_struct
*vma
, unsigned long addr
, bool do_poll
)
443 bool page_was_allocated
;
444 struct page
*retpage
= __read_swap_cache_async(entry
, gfp_mask
,
445 vma
, addr
, &page_was_allocated
);
447 if (page_was_allocated
)
448 swap_readpage(retpage
, do_poll
);
453 static unsigned int __swapin_nr_pages(unsigned long prev_offset
,
454 unsigned long offset
,
459 unsigned int pages
, last_ra
;
462 * This heuristic has been found to work well on both sequential and
463 * random loads, swapping to hard disk or to SSD: please don't ask
464 * what the "+ 2" means, it just happens to work well, that's all.
469 * We can have no readahead hits to judge by: but must not get
470 * stuck here forever, so check for an adjacent offset instead
471 * (and don't even bother to check whether swap type is same).
473 if (offset
!= prev_offset
+ 1 && offset
!= prev_offset
- 1)
476 unsigned int roundup
= 4;
477 while (roundup
< pages
)
482 if (pages
> max_pages
)
485 /* Don't shrink readahead too fast */
486 last_ra
= prev_win
/ 2;
493 static unsigned long swapin_nr_pages(unsigned long offset
)
495 static unsigned long prev_offset
;
496 unsigned int hits
, pages
, max_pages
;
497 static atomic_t last_readahead_pages
;
499 max_pages
= 1 << READ_ONCE(page_cluster
);
503 hits
= atomic_xchg(&swapin_readahead_hits
, 0);
504 pages
= __swapin_nr_pages(prev_offset
, offset
, hits
, max_pages
,
505 atomic_read(&last_readahead_pages
));
507 prev_offset
= offset
;
508 atomic_set(&last_readahead_pages
, pages
);
514 * swap_cluster_readahead - swap in pages in hope we need them soon
515 * @entry: swap entry of this memory
516 * @gfp_mask: memory allocation flags
517 * @vmf: fault information
519 * Returns the struct page for entry and addr, after queueing swapin.
521 * Primitive swap readahead code. We simply read an aligned block of
522 * (1 << page_cluster) entries in the swap area. This method is chosen
523 * because it doesn't cost us any seek time. We also make sure to queue
524 * the 'original' request together with the readahead ones...
526 * This has been extended to use the NUMA policies from the mm triggering
529 * Caller must hold down_read on the vma->vm_mm if vmf->vma is not NULL.
531 struct page
*swap_cluster_readahead(swp_entry_t entry
, gfp_t gfp_mask
,
532 struct vm_fault
*vmf
)
535 unsigned long entry_offset
= swp_offset(entry
);
536 unsigned long offset
= entry_offset
;
537 unsigned long start_offset
, end_offset
;
539 struct swap_info_struct
*si
= swp_swap_info(entry
);
540 struct blk_plug plug
;
541 bool do_poll
= true, page_allocated
;
542 struct vm_area_struct
*vma
= vmf
->vma
;
543 unsigned long addr
= vmf
->address
;
545 mask
= swapin_nr_pages(offset
) - 1;
550 /* Read a page_cluster sized and aligned cluster around offset. */
551 start_offset
= offset
& ~mask
;
552 end_offset
= offset
| mask
;
553 if (!start_offset
) /* First page is swap header. */
555 if (end_offset
>= si
->max
)
556 end_offset
= si
->max
- 1;
558 blk_start_plug(&plug
);
559 for (offset
= start_offset
; offset
<= end_offset
; offset
++) {
560 /* Ok, do the async read-ahead now */
561 page
= __read_swap_cache_async(
562 swp_entry(swp_type(entry
), offset
),
563 gfp_mask
, vma
, addr
, &page_allocated
);
566 if (page_allocated
) {
567 swap_readpage(page
, false);
568 if (offset
!= entry_offset
) {
569 SetPageReadahead(page
);
570 count_vm_event(SWAP_RA
);
575 blk_finish_plug(&plug
);
577 lru_add_drain(); /* Push any new pages onto the LRU now */
579 return read_swap_cache_async(entry
, gfp_mask
, vma
, addr
, do_poll
);
582 int init_swap_address_space(unsigned int type
, unsigned long nr_pages
)
584 struct address_space
*spaces
, *space
;
587 nr
= DIV_ROUND_UP(nr_pages
, SWAP_ADDRESS_SPACE_PAGES
);
588 spaces
= kvcalloc(nr
, sizeof(struct address_space
), GFP_KERNEL
);
591 for (i
= 0; i
< nr
; i
++) {
593 INIT_RADIX_TREE(&space
->i_pages
, GFP_ATOMIC
|__GFP_NOWARN
);
594 atomic_set(&space
->i_mmap_writable
, 0);
595 space
->a_ops
= &swap_aops
;
596 /* swap cache doesn't use writeback related tags */
597 mapping_set_no_writeback_tags(space
);
599 nr_swapper_spaces
[type
] = nr
;
600 rcu_assign_pointer(swapper_spaces
[type
], spaces
);
605 void exit_swap_address_space(unsigned int type
)
607 struct address_space
*spaces
;
609 spaces
= swapper_spaces
[type
];
610 nr_swapper_spaces
[type
] = 0;
611 rcu_assign_pointer(swapper_spaces
[type
], NULL
);
616 static inline void swap_ra_clamp_pfn(struct vm_area_struct
*vma
,
620 unsigned long *start
,
623 *start
= max3(lpfn
, PFN_DOWN(vma
->vm_start
),
624 PFN_DOWN(faddr
& PMD_MASK
));
625 *end
= min3(rpfn
, PFN_DOWN(vma
->vm_end
),
626 PFN_DOWN((faddr
& PMD_MASK
) + PMD_SIZE
));
629 static void swap_ra_info(struct vm_fault
*vmf
,
630 struct vma_swap_readahead
*ra_info
)
632 struct vm_area_struct
*vma
= vmf
->vma
;
633 unsigned long ra_val
;
635 unsigned long faddr
, pfn
, fpfn
;
636 unsigned long start
, end
;
637 pte_t
*pte
, *orig_pte
;
638 unsigned int max_win
, hits
, prev_win
, win
, left
;
643 max_win
= 1 << min_t(unsigned int, READ_ONCE(page_cluster
),
644 SWAP_RA_ORDER_CEILING
);
650 faddr
= vmf
->address
;
651 orig_pte
= pte
= pte_offset_map(vmf
->pmd
, faddr
);
652 entry
= pte_to_swp_entry(*pte
);
653 if ((unlikely(non_swap_entry(entry
)))) {
658 fpfn
= PFN_DOWN(faddr
);
659 ra_val
= GET_SWAP_RA_VAL(vma
);
660 pfn
= PFN_DOWN(SWAP_RA_ADDR(ra_val
));
661 prev_win
= SWAP_RA_WIN(ra_val
);
662 hits
= SWAP_RA_HITS(ra_val
);
663 ra_info
->win
= win
= __swapin_nr_pages(pfn
, fpfn
, hits
,
665 atomic_long_set(&vma
->swap_readahead_info
,
666 SWAP_RA_VAL(faddr
, win
, 0));
673 /* Copy the PTEs because the page table may be unmapped */
675 swap_ra_clamp_pfn(vma
, faddr
, fpfn
, fpfn
+ win
, &start
, &end
);
676 else if (pfn
== fpfn
+ 1)
677 swap_ra_clamp_pfn(vma
, faddr
, fpfn
- win
+ 1, fpfn
+ 1,
680 left
= (win
- 1) / 2;
681 swap_ra_clamp_pfn(vma
, faddr
, fpfn
- left
, fpfn
+ win
- left
,
684 ra_info
->nr_pte
= end
- start
;
685 ra_info
->offset
= fpfn
- start
;
686 pte
-= ra_info
->offset
;
690 tpte
= ra_info
->ptes
;
691 for (pfn
= start
; pfn
!= end
; pfn
++)
697 static struct page
*swap_vma_readahead(swp_entry_t fentry
, gfp_t gfp_mask
,
698 struct vm_fault
*vmf
)
700 struct blk_plug plug
;
701 struct vm_area_struct
*vma
= vmf
->vma
;
707 struct vma_swap_readahead ra_info
= {0,};
709 swap_ra_info(vmf
, &ra_info
);
710 if (ra_info
.win
== 1)
713 blk_start_plug(&plug
);
714 for (i
= 0, pte
= ra_info
.ptes
; i
< ra_info
.nr_pte
;
717 if (pte_none(pentry
))
719 if (pte_present(pentry
))
721 entry
= pte_to_swp_entry(pentry
);
722 if (unlikely(non_swap_entry(entry
)))
724 page
= __read_swap_cache_async(entry
, gfp_mask
, vma
,
725 vmf
->address
, &page_allocated
);
728 if (page_allocated
) {
729 swap_readpage(page
, false);
730 if (i
!= ra_info
.offset
) {
731 SetPageReadahead(page
);
732 count_vm_event(SWAP_RA
);
737 blk_finish_plug(&plug
);
740 return read_swap_cache_async(fentry
, gfp_mask
, vma
, vmf
->address
,
745 * swapin_readahead - swap in pages in hope we need them soon
746 * @entry: swap entry of this memory
747 * @gfp_mask: memory allocation flags
748 * @vmf: fault information
750 * Returns the struct page for entry and addr, after queueing swapin.
752 * It's a main entry function for swap readahead. By the configuration,
753 * it will read ahead blocks by cluster-based(ie, physical disk based)
754 * or vma-based(ie, virtual address based on faulty address) readahead.
756 struct page
*swapin_readahead(swp_entry_t entry
, gfp_t gfp_mask
,
757 struct vm_fault
*vmf
)
759 return swap_use_vma_readahead() ?
760 swap_vma_readahead(entry
, gfp_mask
, vmf
) :
761 swap_cluster_readahead(entry
, gfp_mask
, vmf
);
765 static ssize_t
vma_ra_enabled_show(struct kobject
*kobj
,
766 struct kobj_attribute
*attr
, char *buf
)
768 return sprintf(buf
, "%s\n", enable_vma_readahead
? "true" : "false");
770 static ssize_t
vma_ra_enabled_store(struct kobject
*kobj
,
771 struct kobj_attribute
*attr
,
772 const char *buf
, size_t count
)
774 if (!strncmp(buf
, "true", 4) || !strncmp(buf
, "1", 1))
775 enable_vma_readahead
= true;
776 else if (!strncmp(buf
, "false", 5) || !strncmp(buf
, "0", 1))
777 enable_vma_readahead
= false;
783 static struct kobj_attribute vma_ra_enabled_attr
=
784 __ATTR(vma_ra_enabled
, 0644, vma_ra_enabled_show
,
785 vma_ra_enabled_store
);
787 static struct attribute
*swap_attrs
[] = {
788 &vma_ra_enabled_attr
.attr
,
792 static struct attribute_group swap_attr_group
= {
796 static int __init
swap_init_sysfs(void)
799 struct kobject
*swap_kobj
;
801 swap_kobj
= kobject_create_and_add("swap", mm_kobj
);
803 pr_err("failed to create swap kobject\n");
806 err
= sysfs_create_group(swap_kobj
, &swap_attr_group
);
808 pr_err("failed to register swap group\n");
814 kobject_put(swap_kobj
);
817 subsys_initcall(swap_init_sysfs
);