[RFC 2/4] mm/cpuset: Exclude coherent device memory nodes from mems_allowed

[Anshuman Khandual]

Task's mems_allowed decides the final node mask of nodes from which memory
can be allocated irrespective of the process or VMA based memory policy.
Coherent device memory nodes should not be used for any user space memory
allocation, hence they should not be part of any mems_allowed mask in user
space to begin with. This adds a new function system_ram() which computes
system RAM only node mask and excludes all the coherent memory nodes on the
platform. This resultant system RAM node mask is used instead of N_MEMORY
node mask during cpuset update and mems_allowed initialization. It achieves
isolation of the coherent device memory node from userspace allocations.

Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
---
 include/linux/mm.h   |  1 +
 include/linux/node.h | 12 ++++++++++++
 kernel/cpuset.c      | 12 +++++++-----
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a92c8d7..c40b454 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -446,6 +446,7 @@ static inline int put_page_testzero(struct page *page)
 	return page_ref_dec_and_test(page);
 }
 
+
 /*
  * Try to grab a ref unless the page has a refcount of zero, return false if
  * that is the case.
diff --git a/include/linux/node.h b/include/linux/node.h
index fc319de..99978f9 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -87,4 +87,16 @@ static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
 static inline int arch_check_node_cdm(int nid) {return 0;}
 #endif
 
+static inline nodemask_t ram_nodemask(void)
+{
+#ifdef CONFIG_COHERENT_DEVICE
+	nodemask_t ram_nodes;
+
+	nodes_clear(ram_nodes);
+	nodes_andnot(ram_nodes, node_states[N_MEMORY], node_states[N_COHERENT_DEVICE]);
+	return ram_nodes;
+#else
+	return node_states[N_MEMORY];
+#endif
+}
 #endif /* _LINUX_NODE_H_ */
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 29f815d..bdbe847 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -364,9 +364,11 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
  */
 static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
 {
-	while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
+	nodemask_t ram_nodes = ram_nodemask();
+
+	while (!nodes_intersects(cs->effective_mems, ram_nodes))
 		cs = parent_cs(cs);
-	nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
+	nodes_and(*pmask, cs->effective_mems, ram_nodes);
 }
 
 /*
@@ -2301,7 +2303,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 
 	/* fetch the available cpus/mems and find out which changed how */
 	cpumask_copy(&new_cpus, cpu_active_mask);
-	new_mems = node_states[N_MEMORY];
+	new_mems = ram_nodemask();
 
 	cpus_updated = !cpumask_equal(top_cpuset.effective_cpus, &new_cpus);
 	mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);
@@ -2393,11 +2395,11 @@ static int cpuset_track_online_nodes(struct notifier_block *self,
 void __init cpuset_init_smp(void)
 {
 	cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
-	top_cpuset.mems_allowed = node_states[N_MEMORY];
+	top_cpuset.mems_allowed = ram_nodemask();
 	top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;
 
 	cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
-	top_cpuset.effective_mems = node_states[N_MEMORY];
+	top_cpuset.effective_mems = ram_nodemask();
 
 	register_hotmemory_notifier(&cpuset_track_online_nodes_nb);
 
-- 
1.8.3.1