2 * mm/balloon_compaction.c
4 * Common interface for making balloon pages movable by compaction.
6 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
9 #include <linux/slab.h>
10 #include <linux/export.h>
11 #include <linux/balloon_compaction.h>
14 * balloon_page_enqueue - allocates a new page and inserts it into the balloon
16 * @b_dev_info: balloon device decriptor where we will insert a new page to
18 * Driver must call it to properly allocate a new enlisted balloon page
19 * before definetively 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.
23 struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
26 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
27 __GFP_NOMEMALLOC | __GFP_NORETRY);
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.
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);
44 EXPORT_SYMBOL_GPL(balloon_page_enqueue);
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.
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.
57 struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
59 struct page *page, *tmp;
63 dequeued_page = false;
64 list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
66 * Block others from accessing the 'page' while we get around
67 * establishing additional references and preparing the 'page'
68 * to be released by the balloon driver.
70 if (trylock_page(page)) {
71 #ifdef CONFIG_BALLOON_COMPACTION
72 if (!PagePrivate(page)) {
73 /* raced with isolation */
78 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
79 balloon_page_delete(page);
80 __count_vm_event(BALLOON_DEFLATE);
81 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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.
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))
100 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
105 EXPORT_SYMBOL_GPL(balloon_page_dequeue);
107 #ifdef CONFIG_BALLOON_COMPACTION
109 static inline void __isolate_balloon_page(struct page *page)
111 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
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);
121 static inline void __putback_balloon_page(struct page *page)
123 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
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);
133 /* __isolate_lru_page() counterpart for a ballooned page */
134 bool balloon_page_isolate(struct page *page)
137 * Avoid burning cycles with pages that are yet under __free_pages(),
138 * or just got freed under us.
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.
145 if (likely(get_page_unless_zero(page))) {
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.
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.
157 if (likely(trylock_page(page))) {
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.
163 if (balloon_page_movable(page)) {
164 __isolate_balloon_page(page);
175 /* putback_lru_page() counterpart for a ballooned page */
176 void balloon_page_putback(struct page *page)
179 * 'lock_page()' stabilizes the page and prevents races against
180 * concurrent isolation threads attempting to re-isolate it.
184 if (__is_movable_balloon_page(page)) {
185 __putback_balloon_page(page);
186 /* drop the extra ref count taken for page isolation */
190 dump_page(page, "not movable balloon page");
195 /* move_to_new_page() counterpart for a ballooned page */
196 int balloon_page_migrate(struct page *newpage,
197 struct page *page, enum migrate_mode mode)
199 struct balloon_dev_info *balloon = balloon_page_device(page);
202 VM_BUG_ON_PAGE(!PageLocked(page), page);
203 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
205 if (WARN_ON(!__is_movable_balloon_page(page))) {
206 dump_page(page, "not movable balloon page");
210 if (balloon && balloon->migratepage)
211 rc = balloon->migratepage(balloon, newpage, page, mode);
215 #endif /* CONFIG_BALLOON_COMPACTION */