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 20b51ca..457ed76 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -69,6 +69,7 @@
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 @@
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 c0151ff..4f31a16 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1423,6 +1423,7 @@
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 61d6af7..02b9611 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2469,7 +2469,8 @@
}
/**
- * 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 @@
* 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(¤t->cpuset_mem_spread_rotor);
+}
+
+int cpuset_slab_spread_node(void)
+{
+ return cpuset_spread_node(¤t->cpuset_slab_spread_rotor);
+}
+
EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);
/**
diff --git a/mm/slab.c b/mm/slab.c
index 02786e1..8270ba3 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3219,7 +3219,7 @@
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();
