cpusets: randomize node rotor used in cpuset_mem_spread_node()

[ This patch has already been accepted as commit 0ac0c0d0f837 but later
  reverted (commit 35926ff5fba8) because it itroduced arch specific
  __node_random which was defined only for x86 code so it broke other
  archs.  This is a followup without any arch specific code.  Other than
  that there are no functional changes.]

Some workloads that create a large number of small files tend to assign
too many pages to node 0 (multi-node systems).  Part of the reason is
that the rotor (in cpuset_mem_spread_node()) used to assign nodes starts
at node 0 for newly created tasks.

This patch changes the rotor to be initialized to a random node number
of the cpuset.

[akpm@linux-foundation.org: fix layout]
[Lee.Schermerhorn@hp.com: Define stub numa_random() for !NUMA configuration]
[mhocko@suse.cz: Make it arch independent]
[akpm@linux-foundation.org: fix CONFIG_NUMA=y, MAX_NUMNODES>1 build]
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Paul Menage <menage@google.com>
Cc: Jack Steiner <steiner@sgi.com>
Cc: Robin Holt <holt@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Jack Steiner <steiner@sgi.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Paul Menage <menage@google.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Robin Holt <holt@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 0 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 9c9b7545c810..f8bc977ccbbe 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2460,11 +2460,19 @@ static int cpuset_spread_node(int *rotor)
 
 int cpuset_mem_spread_node(void)
 {
+        if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
+                current->cpuset_mem_spread_rotor =
+                        node_random(&current->mems_allowed);
+
         return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
 }
 
 int cpuset_slab_spread_node(void)
 {
+        if (current->cpuset_slab_spread_rotor == NUMA_NO_NODE)
+                current->cpuset_slab_spread_rotor =
+                        node_random(&current->mems_allowed);
+
         return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 17bf7c8d6511..e33177edb3bf 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1173,6 +1173,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         }
         mpol_fix_fork_child_flag(p);
 #endif
+#ifdef CONFIG_CPUSETS
+        p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
+        p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
+#endif
 #ifdef CONFIG_TRACE_IRQFLAGS
         p->irq_events = 0;
 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW