balloon_compaction.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * mm/balloon_compaction.c
  4 *
  5 * Common interface for making balloon pages movable by compaction.
  6 *
  7 * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com>
  8 */
  9#include <linux/mm.h>
 10#include <linux/slab.h>
 11#include <linux/export.h>
 12#include <linux/balloon_compaction.h>
 13
 14static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
 15				     struct page *page)
 16{
 17	/*
 18	 * Block others from accessing the 'page' when we get around to
 19	 * establishing additional references. We should be the only one
 20	 * holding a reference to the 'page' at this point. If we are not, then
 21	 * memory corruption is possible and we should stop execution.
 22	 */
 23	BUG_ON(!trylock_page(page));
 24	balloon_page_insert(b_dev_info, page);
 25	unlock_page(page);
 26	__count_vm_event(BALLOON_INFLATE);
 27	inc_node_page_state(page, NR_BALLOON_PAGES);
 28}
 29
 30/**
 31 * balloon_page_list_enqueue() - inserts a list of pages into the balloon page
 32 *				 list.
 33 * @b_dev_info: balloon device descriptor where we will insert a new page to
 34 * @pages: pages to enqueue - allocated using balloon_page_alloc.
 35 *
 36 * Driver must call this function to properly enqueue balloon pages before
 37 * definitively removing them from the guest system.
 38 *
 39 * Return: number of pages that were enqueued.
 40 */
 41size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
 42				 struct list_head *pages)
 43{
 44	struct page *page, *tmp;
 45	unsigned long flags;
 46	size_t n_pages = 0;
 47
 48	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 49	list_for_each_entry_safe(page, tmp, pages, lru) {
 50		list_del(&page->lru);
 51		balloon_page_enqueue_one(b_dev_info, page);
 52		n_pages++;
 53	}
 54	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 55	return n_pages;
 56}
 57EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
 58
 59/**
 60 * balloon_page_list_dequeue() - removes pages from balloon's page list and
 61 *				 returns a list of the pages.
 62 * @b_dev_info: balloon device descriptor where we will grab a page from.
 63 * @pages: pointer to the list of pages that would be returned to the caller.
 64 * @n_req_pages: number of requested pages.
 65 *
 66 * Driver must call this function to properly de-allocate a previous enlisted
 67 * balloon pages before definitively releasing it back to the guest system.
 68 * This function tries to remove @n_req_pages from the ballooned pages and
 69 * return them to the caller in the @pages list.
 70 *
 71 * Note that this function may fail to dequeue some pages even if the balloon
 72 * isn't empty - since the page list can be temporarily empty due to compaction
 73 * of isolated pages.
 74 *
 75 * Return: number of pages that were added to the @pages list.
 76 */
 77size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
 78				 struct list_head *pages, size_t n_req_pages)
 79{
 80	struct page *page, *tmp;
 81	unsigned long flags;
 82	size_t n_pages = 0;
 83
 84	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 85	list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
 86		if (n_pages == n_req_pages)
 87			break;
 88
 89		/*
 90		 * Block others from accessing the 'page' while we get around to
 91		 * establishing additional references and preparing the 'page'
 92		 * to be released by the balloon driver.
 93		 */
 94		if (!trylock_page(page))
 95			continue;
 96
 97		list_del(&page->lru);
 98		balloon_page_finalize(page);
 99		__count_vm_event(BALLOON_DEFLATE);
100		list_add(&page->lru, pages);
101		unlock_page(page);
102		dec_node_page_state(page, NR_BALLOON_PAGES);
103		n_pages++;
104	}
105	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
106
107	return n_pages;
108}
109EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
110
111/*
112 * balloon_page_alloc - allocates a new page for insertion into the balloon
113 *			page list.
114 *
115 * Driver must call this function to properly allocate a new balloon page.
116 * Driver must call balloon_page_enqueue before definitively removing the page
117 * from the guest system.
118 *
119 * Return: struct page for the allocated page or NULL on allocation failure.
120 */
121struct page *balloon_page_alloc(void)
122{
123	struct page *page = alloc_page(balloon_mapping_gfp_mask() |
124				       __GFP_NOMEMALLOC | __GFP_NORETRY |
125				       __GFP_NOWARN);
126	return page;
127}
128EXPORT_SYMBOL_GPL(balloon_page_alloc);
129
130/*
131 * balloon_page_enqueue - inserts a new page into the balloon page list.
132 *
133 * @b_dev_info: balloon device descriptor where we will insert a new page
134 * @page: new page to enqueue - allocated using balloon_page_alloc.
135 *
136 * Drivers must call this function to properly enqueue a new allocated balloon
137 * page before definitively removing the page from the guest system.
138 *
139 * Drivers must not call balloon_page_enqueue on pages that have been pushed to
140 * a list with balloon_page_push before removing them with balloon_page_pop. To
141 * enqueue a list of pages, use balloon_page_list_enqueue instead.
142 */
143void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
144			  struct page *page)
145{
146	unsigned long flags;
147
148	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
149	balloon_page_enqueue_one(b_dev_info, page);
150	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
151}
152EXPORT_SYMBOL_GPL(balloon_page_enqueue);
153
154/*
155 * balloon_page_dequeue - removes a page from balloon's page list and returns
156 *			  its address to allow the driver to release the page.
157 * @b_dev_info: balloon device descriptor where we will grab a page from.
158 *
159 * Driver must call this function to properly dequeue a previously enqueued page
160 * before definitively releasing it back to the guest system.
161 *
162 * Caller must perform its own accounting to ensure that this
163 * function is called only if some pages are actually enqueued.
164 *
165 * Note that this function may fail to dequeue some pages even if there are
166 * some enqueued pages - since the page list can be temporarily empty due to
167 * the compaction of isolated pages.
168 *
169 * TODO: remove the caller accounting requirements, and allow caller to wait
170 * until all pages can be dequeued.
171 *
172 * Return: struct page for the dequeued page, or NULL if no page was dequeued.
173 */
174struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
175{
176	unsigned long flags;
177	LIST_HEAD(pages);
178	int n_pages;
179
180	n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);
181
182	if (n_pages != 1) {
183		/*
184		 * If we are unable to dequeue a balloon page because the page
185		 * list is empty and there are no isolated pages, then something
186		 * went out of track and some balloon pages are lost.
187		 * BUG() here, otherwise the balloon driver may get stuck in
188		 * an infinite loop while attempting to release all its pages.
189		 */
190		spin_lock_irqsave(&b_dev_info->pages_lock, flags);
191		if (unlikely(list_empty(&b_dev_info->pages) &&
192			     !b_dev_info->isolated_pages))
193			BUG();
194		spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
195		return NULL;
196	}
197	return list_first_entry(&pages, struct page, lru);
198}
199EXPORT_SYMBOL_GPL(balloon_page_dequeue);
200
201#ifdef CONFIG_BALLOON_COMPACTION
202
203static bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
204
205{
206	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
207	unsigned long flags;
208
209	if (!b_dev_info)
210		return false;
211
212	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
213	list_del(&page->lru);
214	b_dev_info->isolated_pages++;
215	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
216
217	return true;
218}
219
220static void balloon_page_putback(struct page *page)
221{
222	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
223	unsigned long flags;
224
225	/* Isolated balloon pages cannot get deflated. */
226	if (WARN_ON_ONCE(!b_dev_info))
227		return;
228
229	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
230	list_add(&page->lru, &b_dev_info->pages);
231	b_dev_info->isolated_pages--;
232	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
233}
234
235/* move_to_new_page() counterpart for a ballooned page */
236static int balloon_page_migrate(struct page *newpage, struct page *page,
237		enum migrate_mode mode)
238{
239	struct balloon_dev_info *balloon = balloon_page_device(page);
240
241	VM_BUG_ON_PAGE(!PageLocked(page), page);
242	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
243
244	/* Isolated balloon pages cannot get deflated. */
245	if (WARN_ON_ONCE(!balloon))
246		return -EAGAIN;
247
248	return balloon->migratepage(balloon, newpage, page, mode);
249}
250
251const struct movable_operations balloon_mops = {
252	.migrate_page = balloon_page_migrate,
253	.isolate_page = balloon_page_isolate,
254	.putback_page = balloon_page_putback,
255};
256
257static int __init balloon_init(void)
258{
259	return set_movable_ops(&balloon_mops, PGTY_offline);
260}
261core_initcall(balloon_init);
262
263#endif /* CONFIG_BALLOON_COMPACTION */