cpusets: new round-robin rotor for SLAB allocations

We have observed several workloads running on multi-node systems where
memory is assigned unevenly across the nodes in the system.  There are
numerous reasons for this but one is the round-robin rotor in
cpuset_mem_spread_node().

For example, a simple test that writes a multi-page file will allocate
pages on nodes 0 2 4 6 ...  Odd nodes are skipped.  (Sometimes it
allocates on odd nodes & skips even nodes).

An example is shown below.  The program "lfile" writes a file consisting
of 10 pages.  The program then mmaps the file & uses get_mempolicy(...,
MPOL_F_NODE) to determine the nodes where the file pages were allocated.
The output is shown below:

	# ./lfile
	 allocated on nodes: 2 4 6 0 1 2 6 0 2

There is a single rotor that is used for allocating both file pages & slab
pages.  Writing the file allocates both a data page & a slab page
(buffer_head).  This advances the RR rotor 2 nodes for each page
allocated.

A quick confirmation seems to confirm this is the cause of the uneven
allocation:

	# echo 0 >/dev/cpuset/memory_spread_slab
	# ./lfile
	 allocated on nodes: 6 7 8 9 0 1 2 3 4 5

This patch introduces a second rotor that is used for slab allocations.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Acked-by: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 20b51cab65939b8fbe71b767648e2952ae816770..457ed765a116a4c06ecd192e0165cf5af096c818 100644 (file)
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -69,6 +69,7 @@ extern void cpuset_task_status_allowed(struct seq_file *m,
                                        struct task_struct *task);
 
 extern int cpuset_mem_spread_node(void);
+extern int cpuset_slab_spread_node(void);
 
 static inline int cpuset_do_page_mem_spread(void)
 {
@@ -194,6 +195,11 @@ static inline int cpuset_mem_spread_node(void)
        return 0;
 }
 
+static inline int cpuset_slab_spread_node(void)
+{
+       return 0;
+}
+
 static inline int cpuset_do_page_mem_spread(void)
 {
        return 0;

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c0151ffd35419652b5c70f16c27978a62bea0b32..4f31a166b1a185d195d358273f0cb6dfdcc0d5bb 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1423,6 +1423,7 @@ struct task_struct {
        nodemask_t mems_allowed;        /* Protected by alloc_lock */
        int mems_allowed_change_disable;
        int cpuset_mem_spread_rotor;
+       int cpuset_slab_spread_rotor;
 #endif
 #ifdef CONFIG_CGROUPS
        /* Control Group info protected by css_set_lock */

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 61d6af7fa6763c7b41ebba575780111761d0779a..02b9611eadde3ebe638b9c24ffbbb5ec8ada5c06 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2469,7 +2469,8 @@ void cpuset_unlock(void)
 }
 
 /**
- * cpuset_mem_spread_node() - On which node to begin search for a page
+ * cpuset_mem_spread_node() - On which node to begin search for a file page
+ * cpuset_slab_spread_node() - On which node to begin search for a slab page
  *
  * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for
  * tasks in a cpuset with is_spread_page or is_spread_slab set),
@@ -2494,16 +2495,27 @@ void cpuset_unlock(void)
  * See kmem_cache_alloc_node().
  */
 
-int cpuset_mem_spread_node(void)
+static int cpuset_spread_node(int *rotor)
 {
        int node;
 
-       node = next_node(current->cpuset_mem_spread_rotor, current->mems_allowed);
+       node = next_node(*rotor, current->mems_allowed);
        if (node == MAX_NUMNODES)
                node = first_node(current->mems_allowed);
-       current->cpuset_mem_spread_rotor = node;
+       *rotor = node;
        return node;
 }
+
+int cpuset_mem_spread_node(void)
+{
+       return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
+}
+
+int cpuset_slab_spread_node(void)
+{
+       return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
+}
+
 EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);
 
 /**

diff --git a/mm/slab.c b/mm/slab.c
index 02786e1a32d26952d66c2dfff80013adf51ccb9e..8270ba3d19860876b1ac349625ab7d34216b426d 100644 (file)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3219,7 +3219,7 @@ static void *alternate_node_alloc(struct kmem_cache *cachep, gfp_t flags)
        nid_alloc = nid_here = numa_node_id();
        get_mems_allowed();
        if (cpuset_do_slab_mem_spread() && (cachep->flags & SLAB_MEM_SPREAD))
-               nid_alloc = cpuset_mem_spread_node();
+               nid_alloc = cpuset_slab_spread_node();
        else if (current->mempolicy)
                nid_alloc = slab_node(current->mempolicy);
        put_mems_allowed();