mm/mpol: Check for misplaced page

Commit-ID:  147c5c460202df93a9df981cf9f3a84bcb33f998
Gitweb:     http://git.kernel.org/tip/147c5c460202df93a9df981cf9f3a84bcb33f998
Author:     Lee Schermerhorn <[email protected]>
AuthorDate: Wed, 11 Jan 2012 15:48:13 +0100
Committer:  Ingo Molnar <[email protected]>
CommitDate: Fri, 18 May 2012 08:16:17 +0200

mm/mpol: Check for misplaced page

This patch provides a new function to test whether a page resides on a node that is appropriate for the mempolicy for the vma and address where the page is supposed to be mapped. This involves looking up the node where the page belongs. So, the function returns that node so that it may be used to allocated the page without consulting the policy again. Because interleaved and non-interleaved allocations are accounted differently, the function also returns whether or not the new node came from an interleaved policy, if the page is misplaced.

A subsequent patch will call this function from the fault path for stable pages with zero page_mapcount(). Because of this, I don't want to go ahead and allocate the page, e.g., via alloc_page_vma() only to have to free it if it has the correct policy. So, I just mimic the alloc_page_vma() node computation logic--sort of.

Note: we could use this function to implement a MPOL_MF_STRICT behavior when migrating pages to match mbind() mempolicy--e.g., to ensure that pages in an interleaved range are reinterleaved rather than left where they are when they reside on any page in the interleave nodemask.

[ Added MPOL_F_LAZY to trigger migrate-on-fault;
simplified code now that we don't have to bother with special crap for interleaved ]

---
 include/linux/mempolicy.h |    3 ++
 mm/mempolicy.c            |   79 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 0 deletions(-)

index b484ae2..f005c00 100644
@@ -68,6 +68,7 @@ enum mpol_rebind_step {
 #define MPOL_F_SHARED  (1 << 0)	/* identify shared policies */
 #define MPOL_F_LOCAL   (1 << 1)	/* preferred local allocation */
 #define MPOL_F_REBINDING (1 << 2)	/* identify policies in rebinding */
+#define MPOL_F_MOF	(1 << 3) /* this policy wants migrate on fault */
 
 #ifdef __KERNEL__
 

@@ -262,6 +263,8 @@ static inline int vma_migratable(struct vm_area_struct *vma)
 	return 1;
 }
 
+extern int mpol_misplaced(struct page *, struct vm_area_struct *, unsigned long);
+
 #else
 
 struct mempolicy {};