mm: mempolicy: 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.

A subsequent patch will call this function from the fault path.
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.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
[ Added MPOL_F_LAZY to trigger migrate-on-fault;
  simplified code now that we don't have to bother
  with special crap for interleaved ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index e5ccb9ddd90eeb634665e88afd13d56184fff241..c511e25235602bc2af11f495f2d92f59f78ebd2c 100644 (file)
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -198,6 +198,8 @@ 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 {};
@@ -323,5 +325,11 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol,
        return 0;
 }
 
+static inline int mpol_misplaced(struct page *page, struct vm_area_struct *vma,
+                                unsigned long address)
+{
+       return -1; /* no node preference */
+}
+
 #endif /* CONFIG_NUMA */
 #endif

diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
index d23dca8367cc0ffc03d10bc182b2fac9b58ea8d5..472de8a5d37eb5d6a8e3a98a374da8c75fc19c20 100644 (file)
--- a/include/uapi/linux/mempolicy.h
+++ b/include/uapi/linux/mempolicy.h
@@ -61,6 +61,7 @@ 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 */
 
 
 #endif /* _UAPI_LINUX_MEMPOLICY_H */

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index c21e91477c4f0b7dff91f50f16bbdc7242b806ce..df1466d3d2d868091b1558719fc676516e0508f3 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2181,6 +2181,82 @@ static void sp_free(struct sp_node *n)
        kmem_cache_free(sn_cache, n);
 }
 
+/**
+ * mpol_misplaced - check whether current page node is valid in policy
+ *
+ * @page   - page to be checked
+ * @vma    - vm area where page mapped
+ * @addr   - virtual address where page mapped
+ *
+ * Lookup current policy node id for vma,addr and "compare to" page's
+ * node id.
+ *
+ * Returns:
+ *     -1      - not misplaced, page is in the right node
+ *     node    - node id where the page should be
+ *
+ * Policy determination "mimics" alloc_page_vma().
+ * Called from fault path where we know the vma and faulting address.
+ */
+int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long addr)
+{
+       struct mempolicy *pol;
+       struct zone *zone;
+       int curnid = page_to_nid(page);
+       unsigned long pgoff;
+       int polnid = -1;
+       int ret = -1;
+
+       BUG_ON(!vma);
+
+       pol = get_vma_policy(current, vma, addr);
+       if (!(pol->flags & MPOL_F_MOF))
+               goto out;
+
+       switch (pol->mode) {
+       case MPOL_INTERLEAVE:
+               BUG_ON(addr >= vma->vm_end);
+               BUG_ON(addr < vma->vm_start);
+
+               pgoff = vma->vm_pgoff;
+               pgoff += (addr - vma->vm_start) >> PAGE_SHIFT;
+               polnid = offset_il_node(pol, vma, pgoff);
+               break;
+
+       case MPOL_PREFERRED:
+               if (pol->flags & MPOL_F_LOCAL)
+                       polnid = numa_node_id();
+               else
+                       polnid = pol->v.preferred_node;
+               break;
+
+       case MPOL_BIND:
+               /*
+                * allows binding to multiple nodes.
+                * use current page if in policy nodemask,
+                * else select nearest allowed node, if any.
+                * If no allowed nodes, use current [!misplaced].
+                */
+               if (node_isset(curnid, pol->v.nodes))
+                       goto out;
+               (void)first_zones_zonelist(
+                               node_zonelist(numa_node_id(), GFP_HIGHUSER),
+                               gfp_zone(GFP_HIGHUSER),
+                               &pol->v.nodes, &zone);
+               polnid = zone->node;
+               break;
+
+       default:
+               BUG();
+       }
+       if (curnid != polnid)
+               ret = polnid;
+out:
+       mpol_cond_put(pol);
+
+       return ret;
+}
+
 static void sp_delete(struct shared_policy *sp, struct sp_node *n)
 {
        pr_debug("deleting %lx-l%lx\n", n->start, n->end);