1/*
2 *  linux/mm/swap_state.c
3 *
4 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5 *  Swap reorganised 29.12.95, Stephen Tweedie
6 *
7 *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
8 */
9#include <linux/module.h>
10#include <linux/mm.h>
11#include <linux/kernel_stat.h>
12#include <linux/swap.h>
13#include <linux/init.h>
14#include <linux/pagemap.h>
15#include <linux/buffer_head.h>
16#include <linux/backing-dev.h>
17#include <linux/pagevec.h>
18#include <linux/migrate.h>
19
20#include <asm/pgtable.h>
21
22/*
23 * swapper_space is a fiction, retained to simplify the path through
24 * vmscan's shrink_list, to make sync_page look nicer, and to allow
25 * future use of radix_tree tags in the swap cache.
26 */
27static const struct address_space_operations swap_aops = {
28	.writepage	= swap_writepage,
29	.sync_page	= block_sync_page,
30	.set_page_dirty	= __set_page_dirty_nobuffers,
31	.migratepage	= migrate_page,
32};
33
34static struct backing_dev_info swap_backing_dev_info = {
35	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
36	.unplug_io_fn	= swap_unplug_io_fn,
37};
38
39struct address_space swapper_space = {
40	.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
41	.tree_lock	= __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
42	.a_ops		= &swap_aops,
43	.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
44	.backing_dev_info = &swap_backing_dev_info,
45};
46
47#define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
48
49static struct {
50	unsigned long add_total;
51	unsigned long del_total;
52	unsigned long find_success;
53	unsigned long find_total;
54	unsigned long noent_race;
55	unsigned long exist_race;
56} swap_cache_info;
57
58void show_swap_cache_info(void)
59{
60	printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
61		swap_cache_info.add_total, swap_cache_info.del_total,
62		swap_cache_info.find_success, swap_cache_info.find_total,
63		swap_cache_info.noent_race, swap_cache_info.exist_race);
64	printk("Free swap  = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
65	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
66}
67
68/*
69 * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
70 * but sets SwapCache flag and private instead of mapping and index.
71 */
72static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
73			       gfp_t gfp_mask)
74{
75	int error;
76
77	BUG_ON(PageSwapCache(page));
78	BUG_ON(PagePrivate(page));
79	error = radix_tree_preload(gfp_mask);
80	if (!error) {
81		write_lock_irq(&swapper_space.tree_lock);
82		error = radix_tree_insert(&swapper_space.page_tree,
83						entry.val, page);
84		if (!error) {
85			page_cache_get(page);
86			SetPageLocked(page);
87			SetPageSwapCache(page);
88			set_page_private(page, entry.val);
89			total_swapcache_pages++;
90			__inc_zone_page_state(page, NR_FILE_PAGES);
91		}
92		write_unlock_irq(&swapper_space.tree_lock);
93		radix_tree_preload_end();
94	}
95	return error;
96}
97
98static int add_to_swap_cache(struct page *page, swp_entry_t entry)
99{
100	int error;
101
102	if (!swap_duplicate(entry)) {
103		INC_CACHE_INFO(noent_race);
104		return -ENOENT;
105	}
106	error = __add_to_swap_cache(page, entry, GFP_KERNEL);
107	/*
108	 * Anon pages are already on the LRU, we don't run lru_cache_add here.
109	 */
110	if (error) {
111		swap_free(entry);
112		if (error == -EEXIST)
113			INC_CACHE_INFO(exist_race);
114		return error;
115	}
116	INC_CACHE_INFO(add_total);
117	return 0;
118}
119
120/*
121 * This must be called only on pages that have
122 * been verified to be in the swap cache.
123 */
124void __delete_from_swap_cache(struct page *page)
125{
126	BUG_ON(!PageLocked(page));
127	BUG_ON(!PageSwapCache(page));
128	BUG_ON(PageWriteback(page));
129	BUG_ON(PagePrivate(page));
130
131	radix_tree_delete(&swapper_space.page_tree, page_private(page));
132	set_page_private(page, 0);
133	ClearPageSwapCache(page);
134	total_swapcache_pages--;
135	__dec_zone_page_state(page, NR_FILE_PAGES);
136	INC_CACHE_INFO(del_total);
137}
138
139/**
140 * add_to_swap - allocate swap space for a page
141 * @page: page we want to move to swap
142 *
143 * Allocate swap space for the page and add the page to the
144 * swap cache.  Caller needs to hold the page lock.
145 */
146int add_to_swap(struct page * page, gfp_t gfp_mask)
147{
148	swp_entry_t entry;
149	int err;
150
151	BUG_ON(!PageLocked(page));
152
153	for (;;) {
154		entry = get_swap_page();
155		if (!entry.val)
156			return 0;
157
158		/*
159		 * Radix-tree node allocations from PF_MEMALLOC contexts could
160		 * completely exhaust the page allocator. __GFP_NOMEMALLOC
161		 * stops emergency reserves from being allocated.
162		 *
163		 * TODO: this could cause a theoretical memory reclaim
164		 * deadlock in the swap out path.
165		 */
166		/*
167		 * Add it to the swap cache and mark it dirty
168		 */
169		err = __add_to_swap_cache(page, entry,
170				gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
171
172		switch (err) {
173		case 0:				/* Success */
174			SetPageUptodate(page);
175			SetPageDirty(page);
176			INC_CACHE_INFO(add_total);
177			return 1;
178		case -EEXIST:
179			/* Raced with "speculative" read_swap_cache_async */
180			INC_CACHE_INFO(exist_race);
181			swap_free(entry);
182			continue;
183		default:
184			/* -ENOMEM radix-tree allocation failure */
185			swap_free(entry);
186			return 0;
187		}
188	}
189}
190
191/*
192 * This must be called only on pages that have
193 * been verified to be in the swap cache and locked.
194 * It will never put the page into the free list,
195 * the caller has a reference on the page.
196 */
197void delete_from_swap_cache(struct page *page)
198{
199	swp_entry_t entry;
200
201	entry.val = page_private(page);
202
203	write_lock_irq(&swapper_space.tree_lock);
204	__delete_from_swap_cache(page);
205	write_unlock_irq(&swapper_space.tree_lock);
206
207	swap_free(entry);
208	page_cache_release(page);
209}
210
211/*
212 * Strange swizzling function only for use by shmem_writepage
213 */
214int move_to_swap_cache(struct page *page, swp_entry_t entry)
215{
216	int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
217	if (!err) {
218		remove_from_page_cache(page);
219		page_cache_release(page);	/* pagecache ref */
220		if (!swap_duplicate(entry))
221			BUG();
222		SetPageDirty(page);
223		INC_CACHE_INFO(add_total);
224	} else if (err == -EEXIST)
225		INC_CACHE_INFO(exist_race);
226	return err;
227}
228
229/*
230 * Strange swizzling function for shmem_getpage (and shmem_unuse)
231 */
232int move_from_swap_cache(struct page *page, unsigned long index,
233		struct address_space *mapping)
234{
235	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
236	if (!err) {
237		delete_from_swap_cache(page);
238		/* shift page from clean_pages to dirty_pages list */
239		ClearPageDirty(page);
240		set_page_dirty(page);
241	}
242	return err;
243}
244
245/*
246 * If we are the only user, then try to free up the swap cache.
247 *
248 * Its ok to check for PageSwapCache without the page lock
249 * here because we are going to recheck again inside
250 * exclusive_swap_page() _with_ the lock.
251 * 					- Marcelo
252 */
253static inline void free_swap_cache(struct page *page)
254{
255	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
256		remove_exclusive_swap_page(page);
257		unlock_page(page);
258	}
259}
260
261/*
262 * Perform a free_page(), also freeing any swap cache associated with
263 * this page if it is the last user of the page.
264 */
265void free_page_and_swap_cache(struct page *page)
266{
267	free_swap_cache(page);
268	page_cache_release(page);
269}
270
271/*
272 * Passed an array of pages, drop them all from swapcache and then release
273 * them.  They are removed from the LRU and freed if this is their last use.
274 */
275void free_pages_and_swap_cache(struct page **pages, int nr)
276{
277	struct page **pagep = pages;
278
279	lru_add_drain();
280	while (nr) {
281		int todo = min(nr, PAGEVEC_SIZE);
282		int i;
283
284		for (i = 0; i < todo; i++)
285			free_swap_cache(pagep[i]);
286		release_pages(pagep, todo, 0);
287		pagep += todo;
288		nr -= todo;
289	}
290}
291
292/*
293 * Lookup a swap entry in the swap cache. A found page will be returned
294 * unlocked and with its refcount incremented - we rely on the kernel
295 * lock getting page table operations atomic even if we drop the page
296 * lock before returning.
297 */
298struct page * lookup_swap_cache(swp_entry_t entry)
299{
300	struct page *page;
301
302	page = find_get_page(&swapper_space, entry.val);
303
304	if (page)
305		INC_CACHE_INFO(find_success);
306
307	INC_CACHE_INFO(find_total);
308	return page;
309}
310
311/*
312 * Locate a page of swap in physical memory, reserving swap cache space
313 * and reading the disk if it is not already cached.
314 * A failure return means that either the page allocation failed or that
315 * the swap entry is no longer in use.
316 */
317struct page *read_swap_cache_async(swp_entry_t entry,
318			struct vm_area_struct *vma, unsigned long addr)
319{
320	struct page *found_page, *new_page = NULL;
321	int err;
322
323	do {
324		/*
325		 * First check the swap cache.  Since this is normally
326		 * called after lookup_swap_cache() failed, re-calling
327		 * that would confuse statistics.
328		 */
329		found_page = find_get_page(&swapper_space, entry.val);
330		if (found_page)
331			break;
332
333		/*
334		 * Get a new page to read into from swap.
335		 */
336		if (!new_page) {
337			new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
338			if (!new_page)
339				break;		/* Out of memory */
340		}
341
342		/*
343		 * Associate the page with swap entry in the swap cache.
344		 * May fail (-ENOENT) if swap entry has been freed since
345		 * our caller observed it.  May fail (-EEXIST) if there
346		 * is already a page associated with this entry in the
347		 * swap cache: added by a racing read_swap_cache_async,
348		 * or by try_to_swap_out (or shmem_writepage) re-using
349		 * the just freed swap entry for an existing page.
350		 * May fail (-ENOMEM) if radix-tree node allocation failed.
351		 */
352		err = add_to_swap_cache(new_page, entry);
353		if (!err) {
354			/*
355			 * Initiate read into locked page and return.
356			 */
357			lru_cache_add_active(new_page);
358			swap_readpage(NULL, new_page);
359			return new_page;
360		}
361	} while (err != -ENOENT && err != -ENOMEM);
362
363	if (new_page)
364		page_cache_release(new_page);
365	return found_page;
366}
367