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 */