mempolicy: add MPOL_F_RELATIVE_NODES flag

Adds another optional mode flag, MPOL_F_RELATIVE_NODES, that specifies
nodemasks passed via set_mempolicy() or mbind() should be considered relative
to the current task's mems_allowed.

When the mempolicy is created, the passed nodemask is folded and mapped onto
the current task's mems_allowed.  For example, consider a task using
set_mempolicy() to pass MPOL_INTERLEAVE | MPOL_F_RELATIVE_NODES with a
nodemask of 1-3.  If current's mems_allowed is 4-7, the effected nodemask is
5-7 (the second, third, and fourth node of mems_allowed).

If the same task is attached to a cpuset, the mempolicy nodemask is rebound
each time the mems are changed.  Some possible rebinds and results are:

	mems			result
	1-3			1-3
	1-7			2-4
	1,5-6			1,5-6
	1,5-7			5-7

Likewise, the zonelist built for MPOL_BIND acts on the set of zones assigned
to the resultant nodemask from the relative remap.

In the MPOL_PREFERRED case, the preferred node is remapped from the currently
effected nodemask to the relative nodemask.

This mempolicy mode flag was conceived of by Paul Jackson <pj@sgi.com>.

Cc: Paul Jackson <pj@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 31 insertions, 2 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d59b1e766ae..ffd3be66b25 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -136,7 +136,15 @@ static int is_valid_nodemask(nodemask_t *nodemask)
 
 static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
 {
-        return pol->flags & MPOL_F_STATIC_NODES;
+        return pol->flags & (MPOL_F_STATIC_NODES | MPOL_F_RELATIVE_NODES);
+}
+
+static void mpol_relative_nodemask(nodemask_t *ret, const nodemask_t *orig,
+                                   const nodemask_t *rel)
+{
+        nodemask_t tmp;
+        nodes_fold(tmp, *orig, nodes_weight(*rel));
+        nodes_onto(*ret, tmp, *rel);
 }
 
 /* Create a new policy */
@@ -157,7 +165,12 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
                 return ERR_PTR(-ENOMEM);
         atomic_set(&policy->refcnt, 1);
         cpuset_update_task_memory_state();
-        nodes_and(cpuset_context_nmask, *nodes, cpuset_current_mems_allowed);
+        if (flags & MPOL_F_RELATIVE_NODES)
+                mpol_relative_nodemask(&cpuset_context_nmask, nodes,
+                                       &cpuset_current_mems_allowed);
+        else
+                nodes_and(cpuset_context_nmask, *nodes,
+                          cpuset_current_mems_allowed);
         switch (mode) {
         case MPOL_INTERLEAVE:
                 if (nodes_empty(*nodes) || nodes_empty(cpuset_context_nmask))
@@ -873,6 +886,9 @@ asmlinkage long sys_mbind(unsigned long start, unsigned long len,
         mode &= ~MPOL_MODE_FLAGS;
         if (mode >= MPOL_MAX)
                 return -EINVAL;
+        if ((mode_flags & MPOL_F_STATIC_NODES) &&
+            (mode_flags & MPOL_F_RELATIVE_NODES))
+                return -EINVAL;
         err = get_nodes(&nodes, nmask, maxnode);
         if (err)
                 return err;
@@ -891,6 +907,8 @@ asmlinkage long sys_set_mempolicy(int mode, unsigned long __user *nmask,
         mode &= ~MPOL_MODE_FLAGS;
         if ((unsigned int)mode >= MPOL_MAX)
                 return -EINVAL;
+        if ((flags & MPOL_F_STATIC_NODES) && (flags & MPOL_F_RELATIVE_NODES))
+                return -EINVAL;
         err = get_nodes(&nodes, nmask, maxnode);
         if (err)
                 return err;
@@ -1745,10 +1763,12 @@ static void mpol_rebind_policy(struct mempolicy *pol,
 {
         nodemask_t tmp;
         int static_nodes;
+        int relative_nodes;
 
         if (!pol)
                 return;
         static_nodes = pol->flags & MPOL_F_STATIC_NODES;
+        relative_nodes = pol->flags & MPOL_F_RELATIVE_NODES;
         if (!mpol_store_user_nodemask(pol) &&
             nodes_equal(pol->w.cpuset_mems_allowed, *newmask))
                 return;
@@ -1761,6 +1781,9 @@ static void mpol_rebind_policy(struct mempolicy *pol,
         case MPOL_INTERLEAVE:
                 if (static_nodes)
                         nodes_and(tmp, pol->w.user_nodemask, *newmask);
+                else if (relative_nodes)
+                        mpol_relative_nodemask(&tmp, &pol->w.user_nodemask,
+                                               newmask);
                 else {
                         nodes_remap(tmp, pol->v.nodes,
                                     pol->w.cpuset_mems_allowed, *newmask);
@@ -1783,6 +1806,10 @@ static void mpol_rebind_policy(struct mempolicy *pol,
                                 pol->v.preferred_node = node;
                         else
                                 pol->v.preferred_node = -1;
+                } else if (relative_nodes) {
+                        mpol_relative_nodemask(&tmp, &pol->w.user_nodemask,
+                                               newmask);
+                        pol->v.preferred_node = first_node(tmp);
                 } else {
                         pol->v.preferred_node = node_remap(pol->v.preferred_node,
                                         pol->w.cpuset_mems_allowed, *newmask);
@@ -1878,6 +1905,8 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 
                 if (flags & MPOL_F_STATIC_NODES)
                         p += sprintf(p, "%sstatic", need_bar++ ? "|" : "");
+                if (flags & MPOL_F_RELATIVE_NODES)
+                        p += sprintf(p, "%srelative", need_bar++ ? "|" : "");
         }
 
         if (!nodes_empty(nodes)) {