mm/mpol: Add MPOL_MF_LAZY ...

Commit-ID:  84e3a981648d6f4836b499cbe668f68d15527507
Gitweb:     http://git.kernel.org/tip/84e3a981648d6f4836b499cbe668f68d15527507
Author:     Lee Schermerhorn <[email protected]>
AuthorDate: Thu, 12 Jan 2012 12:37:17 +0100
Committer:  Ingo Molnar <[email protected]>
CommitDate: Wed, 26 Sep 2012 11:48:32 +0200

mm/mpol: Add MPOL_MF_LAZY ...

This patch adds another mbind() flag to request "lazy migration". The flag, MPOL_MF_LAZY, modifies MPOL_MF_MOVE* such that the selected pages are simply unmapped from the calling task's page table ['_MOVE] or from all referencing page tables [_MOVE_ALL]. Anon pages will first be added to the swap [or migration?] cache, if necessary. The pages will be migrated in the fault path on "first touch", if the policy dictates at that time.

"Lazy Migration" will allow testing of migrate-on-fault via mbind(). Also allows applications to specify that only subsequently touched pages be migrated to obey new policy, instead of all pages in range. This can be useful for multi-threaded applications working on a large shared data area that is initialized by an initial thread resulting in all pages on one [or a few, if overflowed] nodes. After unmap, the pages in regions assigned to the worker threads will be automatically migrated local to the threads on 1st touch.

---
 include/linux/mempolicy.h |   13 +++++++++--
 mm/mempolicy.c            |   46 ++++++++++++++++++++++++++++----------------
 2 files changed, 39 insertions(+), 20 deletions(-)

index dbd48cc..73683fb 100644
@@ -48,9 +48,16 @@ enum mpol_rebind_step {
 
 /* Flags for mbind */
 #define MPOL_MF_STRICT	(1<<0)	/* Verify existing pages in the mapping */
-#define MPOL_MF_MOVE	(1<<1)	/* Move pages owned by this process to conform to mapping */
-#define MPOL_MF_MOVE_ALL (1<<2)	/* Move every page to conform to mapping */
-#define MPOL_MF_INTERNAL (1<<3)	/* Internal flags start here */
+#define MPOL_MF_MOVE	 (1<<1)	/* Move pages owned by this process to conform
+				   to policy */
+#define MPOL_MF_MOVE_ALL (1<<2)	/* Move every page to conform to policy */
+#define MPOL_MF_LAZY	 (1<<3)	/* Modifies '_MOVE:  lazy migrate on fault */
+#define MPOL_MF_INTERNAL (1<<4)	/* Internal flags start here */
+
+#define MPOL_MF_VALID	(MPOL_MF_STRICT   | 	\
+			 MPOL_MF_MOVE     | 	\
+			 MPOL_MF_MOVE_ALL |	\
+			 MPOL_MF_LAZY)
 
 /*
  * Internal flags that share the struct mempolicy flags word with