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-rw-r--r--include/linux/migrate.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index a4e886d17f87..ce42847ed35f 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -11,8 +11,18 @@ typedef struct page *new_page_t(struct page *, unsigned long private, int **);
* Return values from addresss_space_operations.migratepage():
* - negative errno on page migration failure;
* - zero on page migration success;
+ *
+ * The balloon page migration introduces this special case where a 'distinct'
+ * return code is used to flag a successful page migration to unmap_and_move().
+ * This approach is necessary because page migration can race against balloon
+ * deflation procedure, and for such case we could introduce a nasty page leak
+ * if a successfully migrated balloon page gets released concurrently with
+ * migration's unmap_and_move() wrap-up steps.
*/
#define MIGRATEPAGE_SUCCESS 0
+#define MIGRATEPAGE_BALLOON_SUCCESS 1 /* special ret code for balloon page
+ * sucessful migration case.
+ */
#ifdef CONFIG_MIGRATION