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Subject[patch -mm 1/2] mempolicy: disallow static or relative flags for local preferred mode
MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES don't mean anything for
MPOL_PREFERRED policies that were created with an empty nodemask (for
purely local allocations). They'll never be invalidated because the
allowed mems of a task changes or need to be rebound relative to a
cpuset's placement.

Also fixes a bug identified by Lee Schermerhorn that disallowed empty
nodemasks to be passed to MPOL_PREFERRED to specify local allocations.

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>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
Documentation/vm/numa_memory_policy.txt | 16 ++++++++++++++--
mm/mempolicy.c | 17 ++++++++++++-----
2 files changed, 26 insertions(+), 7 deletions(-)
diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt
--- a/Documentation/vm/numa_memory_policy.txt
+++ b/Documentation/vm/numa_memory_policy.txt
@@ -210,6 +210,12 @@ Components of Memory Policies
local allocation for a specific range of addresses--i.e. for
VMA policies.

+ It is possible for the user to specify that local allocation is
+ always preferred by passing an empty nodemask with this mode.
+ If an empty nodemask is passed, the policy cannot use the
+ MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES flags described
+ below.
+
MPOL_INTERLEAVED: This mode specifies that page allocations be
interleaved, on a page granularity, across the nodes specified in
the policy. This mode also behaves slightly differently, based on
@@ -259,7 +265,10 @@ Components of Memory Policies
occurs over that node. If no nodes from the user's nodemask are
now allowed, the Default behavior is used.

- MPOL_F_STATIC_NODES cannot be used with MPOL_F_RELATIVE_NODES.
+ MPOL_F_STATIC_NODES cannot be combined with the
+ MPOL_F_RELATIVE_NODES flag. It also cannot be used for
+ MPOL_PREFERRED policies that were created with an empty nodemask
+ (local allocation).

MPOL_F_RELATIVE_NODES: This flag specifies that the nodemask passed
by the user will be mapped relative to the set of the task or VMA's
@@ -306,7 +315,10 @@ Components of Memory Policies
set of memory nodes allowed by the task's cpuset, as that may
change over time.

- MPOL_F_RELATIVE_NODES cannot be used with MPOL_F_STATIC_NODES.
+ MPOL_F_RELATIVE_NODES cannot be combined with the
+ MPOL_F_STATIC_NODES flag. It also cannot be used for
+ MPOL_PREFERRED policies that were created with an empty nodemask
+ (local allocation).

MEMORY POLICY APIs

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -151,9 +151,7 @@ static int mpol_new_interleave(struct mempolicy *pol, const nodemask_t *nodes)

static int mpol_new_preferred(struct mempolicy *pol, const nodemask_t *nodes)
{
- if (nodes_empty(*nodes))
- return -EINVAL;
- pol->v.preferred_node = first_node(*nodes);
+ pol->v.preferred_node = !nodes_empty(*nodes) ? first_node(*nodes) : -1;
return 0;
}

@@ -176,7 +174,16 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
pr_debug("setting mode %d flags %d nodes[0] %lx\n",
mode, flags, nodes ? nodes_addr(*nodes)[0] : -1);

- if (nodes && nodes_empty(*nodes) && mode != MPOL_PREFERRED)
+ /*
+ * MPOL_PREFERRED cannot be used with MPOL_F_STATIC_NODES or
+ * MPOL_F_RELATIVE_NODES if the nodemask is empty (local allocation).
+ * All other modes require a valid pointer to a non-empty nodemask.
+ */
+ if (mode == MPOL_PREFERRED) {
+ if (nodes_empty(*nodes) && ((flags & MPOL_F_STATIC_NODES) ||
+ (flags & MPOL_F_RELATIVE_NODES)))
+ return ERR_PTR(-EINVAL);
+ } else if (nodes && nodes_empty(*nodes))
return ERR_PTR(-EINVAL);
if (mode == MPOL_DEFAULT)
return NULL;
@@ -250,7 +257,7 @@ static void mpol_rebind_preferred(struct mempolicy *pol,
} else if (pol->flags & MPOL_F_RELATIVE_NODES) {
mpol_relative_nodemask(&tmp, &pol->w.user_nodemask, nodes);
pol->v.preferred_node = first_node(tmp);
- } else {
+ } else if (pol->v.preferred_node != -1) {
pol->v.preferred_node = node_remap(pol->v.preferred_node,
pol->w.cpuset_mems_allowed,
*nodes);

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