Re: [PATCH 0/5] Direct Migration V9: Overview

[Christoph Lameter <clameter@engr.sgi.com>]

On Wed, 11 Jan 2006, KAMEZAWA Hiroyuki wrote:

> I think  current limitation is just Hugetlb pages and mlocked pages. right ?
> Could you make it clear and add comment or doc before going to -mm ?

These are checked by the code in mm/mempolicy.c. Add some
comments to migrate_pages() stating the limitations.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.15/mm/vmscan.c
===================================================================
--- linux-2.6.15.orig/mm/vmscan.c	2006-01-10 22:13:37.000000000 -0800
+++ linux-2.6.15/mm/vmscan.c	2006-01-10 22:16:45.000000000 -0800
@@ -842,6 +842,12 @@ EXPORT_SYMBOL(migrate_page);
  * are movable anymore because t has become empty
  * or no retryable pages exist anymore.
  *
+ * Limitations:
+ * Cannot migrate mlocked pages because there is a danger
+ * that those may be swapped out. Also cannot migrate
+ * huge pages. We also cannot migrate pages of VMA's with
+ * special attributes (VM_IO, VM_LOCKED, VM_PFNMAP).
+ *
  * Return: Number of pages not migrated when "to" ran empty.
  */
 int migrate_pages(struct list_head *from, struct list_head *to,
-
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