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1/*
2 * mm/balloon_compaction.c
3 *
4 * Common interface for making balloon pages movable by compaction.
5 *
6 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
7 */
8#include <linux/mm.h>
9#include <linux/slab.h>
10#include <linux/export.h>
11#include <linux/balloon_compaction.h>
12
13/*
14 * balloon_page_enqueue - allocates a new page and inserts it into the balloon
15 * page list.
16 * @b_dev_info: balloon device descriptor where we will insert a new page to
17 *
18 * Driver must call it to properly allocate a new enlisted balloon page
19 * before definitively removing it from the guest system.
20 * This function returns the page address for the recently enqueued page or
21 * NULL in the case we fail to allocate a new page this turn.
22 */
23struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
24{
25 unsigned long flags;
26 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
27 __GFP_NOMEMALLOC | __GFP_NORETRY);
28 if (!page)
29 return NULL;
30
31 /*
32 * Block others from accessing the 'page' when we get around to
33 * establishing additional references. We should be the only one
34 * holding a reference to the 'page' at this point.
35 */
36 BUG_ON(!trylock_page(page));
37 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
38 balloon_page_insert(b_dev_info, page);
39 __count_vm_event(BALLOON_INFLATE);
40 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
41 unlock_page(page);
42 return page;
43}
44EXPORT_SYMBOL_GPL(balloon_page_enqueue);
45
46/*
47 * balloon_page_dequeue - removes a page from balloon's page list and returns
48 * the its address to allow the driver release the page.
49 * @b_dev_info: balloon device decriptor where we will grab a page from.
50 *
51 * Driver must call it to properly de-allocate a previous enlisted balloon page
52 * before definetively releasing it back to the guest system.
53 * This function returns the page address for the recently dequeued page or
54 * NULL in the case we find balloon's page list temporarily empty due to
55 * compaction isolated pages.
56 */
57struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
58{
59 struct page *page, *tmp;
60 unsigned long flags;
61 bool dequeued_page;
62
63 dequeued_page = false;
64 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
65 list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
66 /*
67 * Block others from accessing the 'page' while we get around
68 * establishing additional references and preparing the 'page'
69 * to be released by the balloon driver.
70 */
71 if (trylock_page(page)) {
72#ifdef CONFIG_BALLOON_COMPACTION
73 if (!PagePrivate(page)) {
74 /* raced with isolation */
75 unlock_page(page);
76 continue;
77 }
78#endif
79 balloon_page_delete(page);
80 __count_vm_event(BALLOON_DEFLATE);
81 unlock_page(page);
82 dequeued_page = true;
83 break;
84 }
85 }
86 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
87
88 if (!dequeued_page) {
89 /*
90 * If we are unable to dequeue a balloon page because the page
91 * list is empty and there is no isolated pages, then something
92 * went out of track and some balloon pages are lost.
93 * BUG() here, otherwise the balloon driver may get stuck into
94 * an infinite loop while attempting to release all its pages.
95 */
96 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
97 if (unlikely(list_empty(&b_dev_info->pages) &&
98 !b_dev_info->isolated_pages))
99 BUG();
100 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
101 page = NULL;
102 }
103 return page;
104}
105EXPORT_SYMBOL_GPL(balloon_page_dequeue);
106
107#ifdef CONFIG_BALLOON_COMPACTION
108
109static inline void __isolate_balloon_page(struct page *page)
110{
111 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
112 unsigned long flags;
113
114 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
115 ClearPagePrivate(page);
116 list_del(&page->lru);
117 b_dev_info->isolated_pages++;
118 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
119}
120
121static inline void __putback_balloon_page(struct page *page)
122{
123 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
124 unsigned long flags;
125
126 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
127 SetPagePrivate(page);
128 list_add(&page->lru, &b_dev_info->pages);
129 b_dev_info->isolated_pages--;
130 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
131}
132
133/* __isolate_lru_page() counterpart for a ballooned page */
134bool balloon_page_isolate(struct page *page)
135{
136 /*
137 * Avoid burning cycles with pages that are yet under __free_pages(),
138 * or just got freed under us.
139 *
140 * In case we 'win' a race for a balloon page being freed under us and
141 * raise its refcount preventing __free_pages() from doing its job
142 * the put_page() at the end of this block will take care of
143 * release this page, thus avoiding a nasty leakage.
144 */
145 if (likely(get_page_unless_zero(page))) {
146 /*
147 * As balloon pages are not isolated from LRU lists, concurrent
148 * compaction threads can race against page migration functions
149 * as well as race against the balloon driver releasing a page.
150 *
151 * In order to avoid having an already isolated balloon page
152 * being (wrongly) re-isolated while it is under migration,
153 * or to avoid attempting to isolate pages being released by
154 * the balloon driver, lets be sure we have the page lock
155 * before proceeding with the balloon page isolation steps.
156 */
157 if (likely(trylock_page(page))) {
158 /*
159 * A ballooned page, by default, has PagePrivate set.
160 * Prevent concurrent compaction threads from isolating
161 * an already isolated balloon page by clearing it.
162 */
163 if (balloon_page_movable(page)) {
164 __isolate_balloon_page(page);
165 unlock_page(page);
166 return true;
167 }
168 unlock_page(page);
169 }
170 put_page(page);
171 }
172 return false;
173}
174
175/* putback_lru_page() counterpart for a ballooned page */
176void balloon_page_putback(struct page *page)
177{
178 /*
179 * 'lock_page()' stabilizes the page and prevents races against
180 * concurrent isolation threads attempting to re-isolate it.
181 */
182 lock_page(page);
183
184 if (__is_movable_balloon_page(page)) {
185 __putback_balloon_page(page);
186 /* drop the extra ref count taken for page isolation */
187 put_page(page);
188 } else {
189 WARN_ON(1);
190 dump_page(page, "not movable balloon page");
191 }
192 unlock_page(page);
193}
194
195/* move_to_new_page() counterpart for a ballooned page */
196int balloon_page_migrate(struct page *newpage,
197 struct page *page, enum migrate_mode mode)
198{
199 struct balloon_dev_info *balloon = balloon_page_device(page);
200 int rc = -EAGAIN;
201
202 VM_BUG_ON_PAGE(!PageLocked(page), page);
203 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
204
205 if (WARN_ON(!__is_movable_balloon_page(page))) {
206 dump_page(page, "not movable balloon page");
207 return rc;
208 }
209
210 if (balloon && balloon->migratepage)
211 rc = balloon->migratepage(balloon, newpage, page, mode);
212
213 return rc;
214}
215#endif /* CONFIG_BALLOON_COMPACTION */
1/*
2 * mm/balloon_compaction.c
3 *
4 * Common interface for making balloon pages movable by compaction.
5 *
6 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
7 */
8#include <linux/mm.h>
9#include <linux/slab.h>
10#include <linux/export.h>
11#include <linux/balloon_compaction.h>
12
13/*
14 * balloon_page_alloc - allocates a new page for insertion into the balloon
15 * page list.
16 *
17 * Driver must call it to properly allocate a new enlisted balloon page.
18 * Driver must call balloon_page_enqueue before definitively removing it from
19 * the guest system. This function returns the page address for the recently
20 * allocated page or NULL in the case we fail to allocate a new page this turn.
21 */
22struct page *balloon_page_alloc(void)
23{
24 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
25 __GFP_NOMEMALLOC | __GFP_NORETRY);
26 return page;
27}
28EXPORT_SYMBOL_GPL(balloon_page_alloc);
29
30/*
31 * balloon_page_enqueue - allocates a new page and inserts it into the balloon
32 * page list.
33 * @b_dev_info: balloon device descriptor where we will insert a new page to
34 * @page: new page to enqueue - allocated using balloon_page_alloc.
35 *
36 * Driver must call it to properly enqueue a new allocated balloon page
37 * before definitively removing it from the guest system.
38 * This function returns the page address for the recently enqueued page or
39 * NULL in the case we fail to allocate a new page this turn.
40 */
41void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
42 struct page *page)
43{
44 unsigned long flags;
45
46 /*
47 * Block others from accessing the 'page' when we get around to
48 * establishing additional references. We should be the only one
49 * holding a reference to the 'page' at this point.
50 */
51 BUG_ON(!trylock_page(page));
52 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
53 balloon_page_insert(b_dev_info, page);
54 __count_vm_event(BALLOON_INFLATE);
55 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
56 unlock_page(page);
57}
58EXPORT_SYMBOL_GPL(balloon_page_enqueue);
59
60/*
61 * balloon_page_dequeue - removes a page from balloon's page list and returns
62 * the its address to allow the driver release the page.
63 * @b_dev_info: balloon device decriptor where we will grab a page from.
64 *
65 * Driver must call it to properly de-allocate a previous enlisted balloon page
66 * before definetively releasing it back to the guest system.
67 * This function returns the page address for the recently dequeued page or
68 * NULL in the case we find balloon's page list temporarily empty due to
69 * compaction isolated pages.
70 */
71struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
72{
73 struct page *page, *tmp;
74 unsigned long flags;
75 bool dequeued_page;
76
77 dequeued_page = false;
78 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
79 list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
80 /*
81 * Block others from accessing the 'page' while we get around
82 * establishing additional references and preparing the 'page'
83 * to be released by the balloon driver.
84 */
85 if (trylock_page(page)) {
86#ifdef CONFIG_BALLOON_COMPACTION
87 if (PageIsolated(page)) {
88 /* raced with isolation */
89 unlock_page(page);
90 continue;
91 }
92#endif
93 balloon_page_delete(page);
94 __count_vm_event(BALLOON_DEFLATE);
95 unlock_page(page);
96 dequeued_page = true;
97 break;
98 }
99 }
100 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
101
102 if (!dequeued_page) {
103 /*
104 * If we are unable to dequeue a balloon page because the page
105 * list is empty and there is no isolated pages, then something
106 * went out of track and some balloon pages are lost.
107 * BUG() here, otherwise the balloon driver may get stuck into
108 * an infinite loop while attempting to release all its pages.
109 */
110 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
111 if (unlikely(list_empty(&b_dev_info->pages) &&
112 !b_dev_info->isolated_pages))
113 BUG();
114 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
115 page = NULL;
116 }
117 return page;
118}
119EXPORT_SYMBOL_GPL(balloon_page_dequeue);
120
121#ifdef CONFIG_BALLOON_COMPACTION
122
123bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
124
125{
126 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
127 unsigned long flags;
128
129 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
130 list_del(&page->lru);
131 b_dev_info->isolated_pages++;
132 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
133
134 return true;
135}
136
137void balloon_page_putback(struct page *page)
138{
139 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
140 unsigned long flags;
141
142 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
143 list_add(&page->lru, &b_dev_info->pages);
144 b_dev_info->isolated_pages--;
145 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
146}
147
148
149/* move_to_new_page() counterpart for a ballooned page */
150int balloon_page_migrate(struct address_space *mapping,
151 struct page *newpage, struct page *page,
152 enum migrate_mode mode)
153{
154 struct balloon_dev_info *balloon = balloon_page_device(page);
155
156 /*
157 * We can not easily support the no copy case here so ignore it as it
158 * is unlikely to be use with ballon pages. See include/linux/hmm.h for
159 * user of the MIGRATE_SYNC_NO_COPY mode.
160 */
161 if (mode == MIGRATE_SYNC_NO_COPY)
162 return -EINVAL;
163
164 VM_BUG_ON_PAGE(!PageLocked(page), page);
165 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
166
167 return balloon->migratepage(balloon, newpage, page, mode);
168}
169
170const struct address_space_operations balloon_aops = {
171 .migratepage = balloon_page_migrate,
172 .isolate_page = balloon_page_isolate,
173 .putback_page = balloon_page_putback,
174};
175EXPORT_SYMBOL_GPL(balloon_aops);
176
177#endif /* CONFIG_BALLOON_COMPACTION */