1 files changed, 106 insertions, 38 deletions

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index ba739b76e6c5..83a7b614061f 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -11,6 +11,105 @@
 #include <linux/export.h>
 #include <linux/balloon_compaction.h>
 
+static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
+				     struct page *page)
+{
+	/*
+	 * Block others from accessing the 'page' when we get around to
+	 * establishing additional references. We should be the only one
+	 * holding a reference to the 'page' at this point. If we are not, then
+	 * memory corruption is possible and we should stop execution.
+	 */
+	BUG_ON(!trylock_page(page));
+	list_del(&page->lru);
+	balloon_page_insert(b_dev_info, page);
+	unlock_page(page);
+	__count_vm_event(BALLOON_INFLATE);
+}
+
+/**
+ * balloon_page_list_enqueue() - inserts a list of pages into the balloon page
+ *				 list.
+ * @b_dev_info: balloon device descriptor where we will insert a new page to
+ * @pages: pages to enqueue - allocated using balloon_page_alloc.
+ *
+ * Driver must call it to properly enqueue a balloon pages before definitively
+ * removing it from the guest system.
+ *
+ * Return: number of pages that were enqueued.
+ */
+size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
+				 struct list_head *pages)
+{
+	struct page *page, *tmp;
+	unsigned long flags;
+	size_t n_pages = 0;
+
+	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+	list_for_each_entry_safe(page, tmp, pages, lru) {
+		balloon_page_enqueue_one(b_dev_info, page);
+		n_pages++;
+	}
+	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+	return n_pages;
+}
+EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
+
+/**
+ * balloon_page_list_dequeue() - removes pages from balloon's page list and
+ *				 returns a list of the pages.
+ * @b_dev_info: balloon device decriptor where we will grab a page from.
+ * @pages: pointer to the list of pages that would be returned to the caller.
+ * @n_req_pages: number of requested pages.
+ *
+ * Driver must call this function to properly de-allocate a previous enlisted
+ * balloon pages before definetively releasing it back to the guest system.
+ * This function tries to remove @n_req_pages from the ballooned pages and
+ * return them to the caller in the @pages list.
+ *
+ * Note that this function may fail to dequeue some pages temporarily empty due
+ * to compaction isolated pages.
+ *
+ * Return: number of pages that were added to the @pages list.
+ */
+size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
+				 struct list_head *pages, size_t n_req_pages)
+{
+	struct page *page, *tmp;
+	unsigned long flags;
+	size_t n_pages = 0;
+
+	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+	list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
+		if (n_pages == n_req_pages)
+			break;
+
+		/*
+		 * Block others from accessing the 'page' while we get around to
+		 * establishing additional references and preparing the 'page'
+		 * to be released by the balloon driver.
+		 */
+		if (!trylock_page(page))
+			continue;
+
+		if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&
+		    PageIsolated(page)) {
+			/* raced with isolation */
+			unlock_page(page);
+			continue;
+		}
+		balloon_page_delete(page);
+		__count_vm_event(BALLOON_DEFLATE);
+		list_add(&page->lru, pages);
+		unlock_page(page);
+		n_pages++;
+	}
+	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+
+	return n_pages;
+}
+EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
+
 /*
  * balloon_page_alloc - allocates a new page for insertion into the balloon
  *			  page list.
@@ -44,17 +143,9 @@ void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
 {
 	unsigned long flags;
 
-	/*
-	 * Block others from accessing the 'page' when we get around to
-	 * establishing additional references. We should be the only one
-	 * holding a reference to the 'page' at this point.
-	 */
-	BUG_ON(!trylock_page(page));
 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
-	balloon_page_insert(b_dev_info, page);
-	__count_vm_event(BALLOON_INFLATE);
+	balloon_page_enqueue_one(b_dev_info, page);
 	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
-	unlock_page(page);
 }
 EXPORT_SYMBOL_GPL(balloon_page_enqueue);
 
@@ -71,36 +162,13 @@ EXPORT_SYMBOL_GPL(balloon_page_enqueue);
  */
 struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
 {
-	struct page *page, *tmp;
 	unsigned long flags;
-	bool dequeued_page;
+	LIST_HEAD(pages);
+	int n_pages;
 
-	dequeued_page = false;
-	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
-	list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
-		/*
-		 * Block others from accessing the 'page' while we get around
-		 * establishing additional references and preparing the 'page'
-		 * to be released by the balloon driver.
-		 */
-		if (trylock_page(page)) {
-#ifdef CONFIG_BALLOON_COMPACTION
-			if (PageIsolated(page)) {
-				/* raced with isolation */
-				unlock_page(page);
-				continue;
-			}
-#endif
-			balloon_page_delete(page);
-			__count_vm_event(BALLOON_DEFLATE);
-			unlock_page(page);
-			dequeued_page = true;
-			break;
-		}
-	}
-	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+	n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);
 
-	if (!dequeued_page) {
+	if (n_pages != 1) {
 		/*
 		 * If we are unable to dequeue a balloon page because the page
 		 * list is empty and there is no isolated pages, then something
@@ -113,9 +181,9 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
 			     !b_dev_info->isolated_pages))
 			BUG();
 		spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
-		page = NULL;
+		return NULL;
 	}
-	return page;
+	return list_first_entry(&pages, struct page, lru);
 }
 EXPORT_SYMBOL_GPL(balloon_page_dequeue);