Commit 0ac0c0d0 authored by Jack Steiner's avatar Jack Steiner Committed by Linus Torvalds
Browse files

cpusets: randomize node rotor used in cpuset_mem_spread_node()

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.

[ fix layout]
[ Define stub numa_random() for !NUMA configuration]
Signed-off-by: default avatarJack Steiner <>
Signed-off-by: default avatarLee Schermerhorn <>
Cc: Christoph Lameter <>
Cc: Pekka Enberg <>
Cc: Paul Menage <>
Cc: Jack Steiner <>
Cc: Robin Holt <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 6adef3eb
......@@ -2,6 +2,7 @@
#include <linux/topology.h>
#include <linux/module.h>
#include <linux/bootmem.h>
#include <linux/random.h>
# define DBG(x...) printk(KERN_DEBUG x)
......@@ -65,3 +66,19 @@ const struct cpumask *cpumask_of_node(int node)
* Return the bit number of a random bit set in the nodemask.
* (returns -1 if nodemask is empty)
int __node_random(const nodemask_t *maskp)
int w, bit = -1;
w = nodes_weight(*maskp);
if (w)
bit = bitmap_ord_to_pos(maskp->bits,
get_random_int() % w, MAX_NUMNODES);
return bit;
......@@ -141,6 +141,7 @@ extern int bitmap_find_free_region(unsigned long *bitmap, int bits, int order);
extern void bitmap_release_region(unsigned long *bitmap, int pos, int order);
extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
extern void bitmap_copy_le(void *dst, const unsigned long *src, int nbits);
extern int bitmap_ord_to_pos(const unsigned long *bitmap, int n, int bits);
#define BITMAP_LAST_WORD_MASK(nbits) \
( \
......@@ -66,6 +66,8 @@
* int num_online_nodes() Number of online Nodes
* int num_possible_nodes() Number of all possible Nodes
* int node_random(mask) Random node with set bit in mask
* int node_online(node) Is some node online?
* int node_possible(node) Is some node possible?
......@@ -430,6 +432,10 @@ static inline void node_set_offline(int nid)
node_clear_state(nid, N_ONLINE);
nr_online_nodes = num_node_state(N_ONLINE);
#define node_random(mask) __node_random(&(mask))
extern int __node_random(const nodemask_t *maskp);
static inline int node_state(int node, enum node_states state)
......@@ -460,6 +466,8 @@ static inline int num_node_state(enum node_states state)
#define node_set_online(node) node_set_state((node), N_ONLINE)
#define node_set_offline(node) node_clear_state((node), N_ONLINE)
static inline int node_random(const nodemask_t mask) { return 0; }
#define node_online_map node_states[N_ONLINE]
......@@ -1079,6 +1079,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->cpuset_mem_spread_rotor = node_random(p->mems_allowed);
p->cpuset_slab_spread_rotor = node_random(p->mems_allowed);
p->irq_events = 0;
......@@ -672,7 +672,7 @@ static int bitmap_pos_to_ord(const unsigned long *buf, int pos, int bits)
* The bit positions 0 through @bits are valid positions in @buf.
static int bitmap_ord_to_pos(const unsigned long *buf, int ord, int bits)
int bitmap_ord_to_pos(const unsigned long *buf, int ord, int bits)
int pos = 0;
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