xref: /openbmc/linux/mm/swap_state.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
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 
18 #include <asm/pgtable.h>
19 
20 /*
21  * swapper_space is a fiction, retained to simplify the path through
22  * vmscan's shrink_list, to make sync_page look nicer, and to allow
23  * future use of radix_tree tags in the swap cache.
24  */
25 static struct address_space_operations swap_aops = {
26 	.writepage	= swap_writepage,
27 	.sync_page	= block_sync_page,
28 	.set_page_dirty	= __set_page_dirty_nobuffers,
29 };
30 
31 static struct backing_dev_info swap_backing_dev_info = {
32 	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
33 	.unplug_io_fn	= swap_unplug_io_fn,
34 };
35 
36 struct address_space swapper_space = {
37 	.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
38 	.tree_lock	= RW_LOCK_UNLOCKED,
39 	.a_ops		= &swap_aops,
40 	.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
41 	.backing_dev_info = &swap_backing_dev_info,
42 };
43 EXPORT_SYMBOL(swapper_space);
44 
45 #define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
46 
47 static struct {
48 	unsigned long add_total;
49 	unsigned long del_total;
50 	unsigned long find_success;
51 	unsigned long find_total;
52 	unsigned long noent_race;
53 	unsigned long exist_race;
54 } swap_cache_info;
55 
56 void show_swap_cache_info(void)
57 {
58 	printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
59 		swap_cache_info.add_total, swap_cache_info.del_total,
60 		swap_cache_info.find_success, swap_cache_info.find_total,
61 		swap_cache_info.noent_race, swap_cache_info.exist_race);
62 	printk("Free swap  = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
63 	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
64 }
65 
66 /*
67  * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
68  * but sets SwapCache flag and private instead of mapping and index.
69  */
70 static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
71 			       gfp_t gfp_mask)
72 {
73 	int error;
74 
75 	BUG_ON(PageSwapCache(page));
76 	BUG_ON(PagePrivate(page));
77 	error = radix_tree_preload(gfp_mask);
78 	if (!error) {
79 		write_lock_irq(&swapper_space.tree_lock);
80 		error = radix_tree_insert(&swapper_space.page_tree,
81 						entry.val, page);
82 		if (!error) {
83 			page_cache_get(page);
84 			SetPageLocked(page);
85 			SetPageSwapCache(page);
86 			set_page_private(page, entry.val);
87 			total_swapcache_pages++;
88 			pagecache_acct(1);
89 		}
90 		write_unlock_irq(&swapper_space.tree_lock);
91 		radix_tree_preload_end();
92 	}
93 	return error;
94 }
95 
96 static int add_to_swap_cache(struct page *page, swp_entry_t entry)
97 {
98 	int error;
99 
100 	if (!swap_duplicate(entry)) {
101 		INC_CACHE_INFO(noent_race);
102 		return -ENOENT;
103 	}
104 	error = __add_to_swap_cache(page, entry, GFP_KERNEL);
105 	/*
106 	 * Anon pages are already on the LRU, we don't run lru_cache_add here.
107 	 */
108 	if (error) {
109 		swap_free(entry);
110 		if (error == -EEXIST)
111 			INC_CACHE_INFO(exist_race);
112 		return error;
113 	}
114 	INC_CACHE_INFO(add_total);
115 	return 0;
116 }
117 
118 /*
119  * This must be called only on pages that have
120  * been verified to be in the swap cache.
121  */
122 void __delete_from_swap_cache(struct page *page)
123 {
124 	BUG_ON(!PageLocked(page));
125 	BUG_ON(!PageSwapCache(page));
126 	BUG_ON(PageWriteback(page));
127 	BUG_ON(PagePrivate(page));
128 
129 	radix_tree_delete(&swapper_space.page_tree, page_private(page));
130 	set_page_private(page, 0);
131 	ClearPageSwapCache(page);
132 	total_swapcache_pages--;
133 	pagecache_acct(-1);
134 	INC_CACHE_INFO(del_total);
135 }
136 
137 /**
138  * add_to_swap - allocate swap space for a page
139  * @page: page we want to move to swap
140  *
141  * Allocate swap space for the page and add the page to the
142  * swap cache.  Caller needs to hold the page lock.
143  */
144 int add_to_swap(struct page * page)
145 {
146 	swp_entry_t entry;
147 	int err;
148 
149 	if (!PageLocked(page))
150 		BUG();
151 
152 	for (;;) {
153 		entry = get_swap_page();
154 		if (!entry.val)
155 			return 0;
156 
157 		/*
158 		 * Radix-tree node allocations from PF_MEMALLOC contexts could
159 		 * completely exhaust the page allocator. __GFP_NOMEMALLOC
160 		 * stops emergency reserves from being allocated.
161 		 *
162 		 * TODO: this could cause a theoretical memory reclaim
163 		 * deadlock in the swap out path.
164 		 */
165 		/*
166 		 * Add it to the swap cache and mark it dirty
167 		 */
168 		err = __add_to_swap_cache(page, entry,
169 				GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_NOWARN);
170 
171 		switch (err) {
172 		case 0:				/* Success */
173 			SetPageUptodate(page);
174 			SetPageDirty(page);
175 			INC_CACHE_INFO(add_total);
176 			return 1;
177 		case -EEXIST:
178 			/* Raced with "speculative" read_swap_cache_async */
179 			INC_CACHE_INFO(exist_race);
180 			swap_free(entry);
181 			continue;
182 		default:
183 			/* -ENOMEM radix-tree allocation failure */
184 			swap_free(entry);
185 			return 0;
186 		}
187 	}
188 }
189 
190 /*
191  * This must be called only on pages that have
192  * been verified to be in the swap cache and locked.
193  * It will never put the page into the free list,
194  * the caller has a reference on the page.
195  */
196 void delete_from_swap_cache(struct page *page)
197 {
198 	swp_entry_t entry;
199 
200 	entry.val = page_private(page);
201 
202 	write_lock_irq(&swapper_space.tree_lock);
203 	__delete_from_swap_cache(page);
204 	write_unlock_irq(&swapper_space.tree_lock);
205 
206 	swap_free(entry);
207 	page_cache_release(page);
208 }
209 
210 /*
211  * Strange swizzling function only for use by shmem_writepage
212  */
213 int move_to_swap_cache(struct page *page, swp_entry_t entry)
214 {
215 	int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
216 	if (!err) {
217 		remove_from_page_cache(page);
218 		page_cache_release(page);	/* pagecache ref */
219 		if (!swap_duplicate(entry))
220 			BUG();
221 		SetPageDirty(page);
222 		INC_CACHE_INFO(add_total);
223 	} else if (err == -EEXIST)
224 		INC_CACHE_INFO(exist_race);
225 	return err;
226 }
227 
228 /*
229  * Strange swizzling function for shmem_getpage (and shmem_unuse)
230  */
231 int move_from_swap_cache(struct page *page, unsigned long index,
232 		struct address_space *mapping)
233 {
234 	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
235 	if (!err) {
236 		delete_from_swap_cache(page);
237 		/* shift page from clean_pages to dirty_pages list */
238 		ClearPageDirty(page);
239 		set_page_dirty(page);
240 	}
241 	return err;
242 }
243 
244 /*
245  * If we are the only user, then try to free up the swap cache.
246  *
247  * Its ok to check for PageSwapCache without the page lock
248  * here because we are going to recheck again inside
249  * exclusive_swap_page() _with_ the lock.
250  * 					- Marcelo
251  */
252 static inline void free_swap_cache(struct page *page)
253 {
254 	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
255 		remove_exclusive_swap_page(page);
256 		unlock_page(page);
257 	}
258 }
259 
260 /*
261  * Perform a free_page(), also freeing any swap cache associated with
262  * this page if it is the last user of the page.
263  */
264 void free_page_and_swap_cache(struct page *page)
265 {
266 	free_swap_cache(page);
267 	page_cache_release(page);
268 }
269 
270 /*
271  * Passed an array of pages, drop them all from swapcache and then release
272  * them.  They are removed from the LRU and freed if this is their last use.
273  */
274 void free_pages_and_swap_cache(struct page **pages, int nr)
275 {
276 	int chunk = 16;
277 	struct page **pagep = pages;
278 
279 	lru_add_drain();
280 	while (nr) {
281 		int todo = min(chunk, nr);
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  */
298 struct 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  */
317 struct 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