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 */