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@xxxxxxx>
---
include/linux/cpuset.h | 6 ++++++
include/linux/sched.h | 1 +
kernel/cpuset.c | 20 ++++++++++++++++----
mm/slab.c | 2 +-
4 files changed, 24 insertions(+), 5 deletions(-)
Index: linux/include/linux/cpuset.h
===================================================================
--- linux.orig/include/linux/cpuset.h 2010-04-26 14:03:40.000000000 -0500
+++ linux/include/linux/cpuset.h 2010-04-26 15:05:02.574948748 -0500
@@ -69,6 +69,7 @@ extern void cpuset_task_status_allowed(s
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)
{
@@ -158,6 +159,11 @@ static inline int cpuset_mem_spread_node
{
return 0;
}
+
+static inline int cpuset_slab_spread_node(void)
+{
+ return 0;
+}
static inline int cpuset_do_page_mem_spread(void)
{
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h 2010-04-26 14:03:40.000000000 -0500
+++ linux/include/linux/sched.h 2010-04-26 15:04:38.208227585 -0500
@@ -1421,6 +1421,7 @@ struct task_struct {
#ifdef CONFIG_CPUSETS
nodemask_t mems_allowed; /* Protected by alloc_lock */
int cpuset_mem_spread_rotor;
+ int cpuset_slab_spread_rotor;
#endif
#ifdef CONFIG_CGROUPS
/* Control Group info protected by css_set_lock */
Index: linux/kernel/cpuset.c
===================================================================
--- linux.orig/kernel/cpuset.c 2010-04-26 14:03:40.000000000 -0500
+++ linux/kernel/cpuset.c 2010-04-26 15:04:38.246928404 -0500
@@ -2427,7 +2427,8 @@ 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),
@@ -2452,16 +2453,27 @@ 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(¤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);
/**
Index: linux/mm/slab.c
===================================================================
--- linux.orig/mm/slab.c 2010-04-26 14:03:40.000000000 -0500
+++ linux/mm/slab.c 2010-04-26 15:05:34.343755521 -0500
@@ -3242,7 +3242,7 @@ static void *alternate_node_alloc(struct
return NULL;
nid_alloc = nid_here = numa_node_id();
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);
if (nid_alloc != nid_here)
--
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