2 * include/linux/balloon_compaction.h
4 * Common interface definitions for making balloon pages movable by compaction.
6 * Despite being perfectly possible to perform ballooned pages migration, they
7 * make a special corner case to compaction scans because balloon pages are not
8 * enlisted at any LRU list like the other pages we do compact / migrate.
10 * As the page isolation scanning step a compaction thread does is a lockless
11 * procedure (from a page standpoint), it might bring some racy situations while
12 * performing balloon page compaction. In order to sort out these racy scenarios
13 * and safely perform balloon's page compaction and migration we must, always,
14 * ensure following these three simple rules:
16 * i. when updating a balloon's page ->mapping element, strictly do it under
17 * the following lock order, independently of the far superior
18 * locking scheme (lru_lock, balloon_lock):
20 * +--spin_lock_irq(&b_dev_info->pages_lock);
21 * ... page->mapping updates here ...
23 * ii. before isolating or dequeueing a balloon page from the balloon device
24 * pages list, the page reference counter must be raised by one and the
25 * extra refcount must be dropped when the page is enqueued back into
26 * the balloon device page list, thus a balloon page keeps its reference
27 * counter raised only while it is under our special handling;
29 * iii. after the lockless scan step have selected a potential balloon page for
30 * isolation, re-test the page->mapping flags and the page ref counter
31 * under the proper page lock, to ensure isolating a valid balloon page
32 * (not yet isolated, nor under release procedure)
34 * The functions provided by this interface are placed to help on coping with
35 * the aforementioned balloon page corner case, as well as to ensure the simple
36 * set of exposed rules are satisfied while we are dealing with balloon pages
37 * compaction / migration.
39 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
41 #ifndef _LINUX_BALLOON_COMPACTION_H
42 #define _LINUX_BALLOON_COMPACTION_H
43 #include <linux/pagemap.h>
44 #include <linux/page-flags.h>
45 #include <linux/migrate.h>
46 #include <linux/gfp.h>
47 #include <linux/err.h>
50 * Balloon device information descriptor.
51 * This struct is used to allow the common balloon compaction interface
52 * procedures to find the proper balloon device holding memory pages they'll
53 * have to cope for page compaction / migration, as well as it serves the
54 * balloon driver as a page book-keeper for its registered balloon devices.
56 struct balloon_dev_info
{
57 void *balloon_device
; /* balloon device descriptor */
58 struct address_space
*mapping
; /* balloon special page->mapping */
59 unsigned long isolated_pages
; /* # of isolated pages for migration */
60 spinlock_t pages_lock
; /* Protection to pages list */
61 struct list_head pages
; /* Pages enqueued & handled to Host */
64 extern struct page
*balloon_page_enqueue(struct balloon_dev_info
*b_dev_info
);
65 extern struct page
*balloon_page_dequeue(struct balloon_dev_info
*b_dev_info
);
66 extern struct balloon_dev_info
*balloon_devinfo_alloc(
67 void *balloon_dev_descriptor
);
69 static inline void balloon_devinfo_free(struct balloon_dev_info
*b_dev_info
)
75 * balloon_page_free - release a balloon page back to the page free lists
76 * @page: ballooned page to be set free
78 * This function must be used to properly set free an isolated/dequeued balloon
79 * page at the end of a sucessful page migration, or at the balloon driver's
80 * page release procedure.
82 static inline void balloon_page_free(struct page
*page
)
85 * Balloon pages always get an extra refcount before being isolated
86 * and before being dequeued to help on sorting out fortuite colisions
87 * between a thread attempting to isolate and another thread attempting
88 * to release the very same balloon page.
90 * Before we handle the page back to Buddy, lets drop its extra refcnt.
96 #ifdef CONFIG_BALLOON_COMPACTION
97 extern bool balloon_page_isolate(struct page
*page
);
98 extern void balloon_page_putback(struct page
*page
);
99 extern int balloon_page_migrate(struct page
*newpage
,
100 struct page
*page
, enum migrate_mode mode
);
101 extern struct address_space
102 *balloon_mapping_alloc(struct balloon_dev_info
*b_dev_info
,
103 const struct address_space_operations
*a_ops
);
105 static inline void balloon_mapping_free(struct address_space
*balloon_mapping
)
107 kfree(balloon_mapping
);
111 * page_flags_cleared - helper to perform balloon @page ->flags tests.
113 * As balloon pages are obtained from buddy and we do not play with page->flags
114 * at driver level (exception made when we get the page lock for compaction),
115 * we can safely identify a ballooned page by checking if the
116 * PAGE_FLAGS_CHECK_AT_PREP page->flags are all cleared. This approach also
117 * helps us skip ballooned pages that are locked for compaction or release, thus
118 * mitigating their racy check at balloon_page_movable()
120 static inline bool page_flags_cleared(struct page
*page
)
122 return !(page
->flags
& PAGE_FLAGS_CHECK_AT_PREP
);
126 * __is_movable_balloon_page - helper to perform @page mapping->flags tests
128 static inline bool __is_movable_balloon_page(struct page
*page
)
130 struct address_space
*mapping
= page
->mapping
;
131 return mapping_balloon(mapping
);
135 * balloon_page_movable - test page->mapping->flags to identify balloon pages
136 * that can be moved by compaction/migration.
138 * This function is used at core compaction's page isolation scheme, therefore
139 * most pages exposed to it are not enlisted as balloon pages and so, to avoid
140 * undesired side effects like racing against __free_pages(), we cannot afford
141 * holding the page locked while testing page->mapping->flags here.
143 * As we might return false positives in the case of a balloon page being just
144 * released under us, the page->mapping->flags need to be re-tested later,
145 * under the proper page lock, at the functions that will be coping with the
148 static inline bool balloon_page_movable(struct page
*page
)
151 * Before dereferencing and testing mapping->flags, let's make sure
152 * this is not a page that uses ->mapping in a different way
154 if (page_flags_cleared(page
) && !page_mapped(page
) &&
155 page_count(page
) == 1)
156 return __is_movable_balloon_page(page
);
162 * balloon_page_insert - insert a page into the balloon's page list and make
163 * the page->mapping assignment accordingly.
164 * @page : page to be assigned as a 'balloon page'
165 * @mapping : allocated special 'balloon_mapping'
166 * @head : balloon's device page list head
168 * Caller must ensure the page is locked and the spin_lock protecting balloon
169 * pages list is held before inserting a page into the balloon device.
171 static inline void balloon_page_insert(struct page
*page
,
172 struct address_space
*mapping
,
173 struct list_head
*head
)
175 page
->mapping
= mapping
;
176 list_add(&page
->lru
, head
);
180 * balloon_page_delete - delete a page from balloon's page list and clear
181 * the page->mapping assignement accordingly.
182 * @page : page to be released from balloon's page list
184 * Caller must ensure the page is locked and the spin_lock protecting balloon
185 * pages list is held before deleting a page from the balloon device.
187 static inline void balloon_page_delete(struct page
*page
)
189 page
->mapping
= NULL
;
190 list_del(&page
->lru
);
194 * balloon_page_device - get the b_dev_info descriptor for the balloon device
195 * that enqueues the given page.
197 static inline struct balloon_dev_info
*balloon_page_device(struct page
*page
)
199 struct address_space
*mapping
= page
->mapping
;
201 return mapping
->private_data
;
206 static inline gfp_t
balloon_mapping_gfp_mask(void)
208 return GFP_HIGHUSER_MOVABLE
;
211 static inline bool balloon_compaction_check(void)
216 #else /* !CONFIG_BALLOON_COMPACTION */
218 static inline void *balloon_mapping_alloc(void *balloon_device
,
219 const struct address_space_operations
*a_ops
)
221 return ERR_PTR(-EOPNOTSUPP
);
224 static inline void balloon_mapping_free(struct address_space
*balloon_mapping
)
229 static inline void balloon_page_insert(struct page
*page
,
230 struct address_space
*mapping
,
231 struct list_head
*head
)
233 list_add(&page
->lru
, head
);
236 static inline void balloon_page_delete(struct page
*page
)
238 list_del(&page
->lru
);
241 static inline bool balloon_page_movable(struct page
*page
)
246 static inline bool balloon_page_isolate(struct page
*page
)
251 static inline void balloon_page_putback(struct page
*page
)
256 static inline int balloon_page_migrate(struct page
*newpage
,
257 struct page
*page
, enum migrate_mode mode
)
262 static inline gfp_t
balloon_mapping_gfp_mask(void)
267 static inline bool balloon_compaction_check(void)
271 #endif /* CONFIG_BALLOON_COMPACTION */
272 #endif /* _LINUX_BALLOON_COMPACTION_H */
This page took 0.036729 seconds and 5 git commands to generate.