Merge tag 'upstream-4.9-rc3' of git://git.infradead.org/linux-ubifs

[cascardo/linux.git] / include / linux / compaction.h

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index e88c037..0d84158 100644 (file)
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -6,8 +6,10 @@
  * Lower value means higher priority, analogically to reclaim priority.
  */
 enum compact_priority {
+       COMPACT_PRIO_SYNC_FULL,
+       MIN_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_FULL,
        COMPACT_PRIO_SYNC_LIGHT,
-       MIN_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_LIGHT,
+       MIN_COMPACT_COSTLY_PRIORITY = COMPACT_PRIO_SYNC_LIGHT,
        DEF_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_LIGHT,
        COMPACT_PRIO_ASYNC,
        INIT_COMPACT_PRIORITY = COMPACT_PRIO_ASYNC
@@ -57,6 +59,29 @@ enum compact_result {
 
 struct alloc_context; /* in mm/internal.h */
 
+/*
+ * Number of free order-0 pages that should be available above given watermark
+ * to make sure compaction has reasonable chance of not running out of free
+ * pages that it needs to isolate as migration target during its work.
+ */
+static inline unsigned long compact_gap(unsigned int order)
+{
+       /*
+        * Although all the isolations for migration are temporary, compaction
+        * free scanner may have up to 1 << order pages on its list and then
+        * try to split an (order - 1) free page. At that point, a gap of
+        * 1 << order might not be enough, so it's safer to require twice that
+        * amount. Note that the number of pages on the list is also
+        * effectively limited by COMPACT_CLUSTER_MAX, as that's the maximum
+        * that the migrate scanner can have isolated on migrate list, and free
+        * scanner is only invoked when the number of isolated free pages is
+        * lower than that. But it's not worth to complicate the formula here
+        * as a bigger gap for higher orders than strictly necessary can also
+        * improve chances of compaction success.
+        */
+       return 2UL << order;
+}
+
 #ifdef CONFIG_COMPACTION
 extern int sysctl_compact_memory;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,