[This patch has already been accepted as 0ac0c0d but later reverted

(35926ff) 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]
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 907dd58aa2289428e47911387c2d033edc1b7045..7ad634501e48cd7d39b1e8b621f0affce26765d7 100644 (file)
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -144,6 +144,7 @@ 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_FIRST_WORD_MASK(start) (~0UL << ((start) % BITS_PER_LONG))
 #define BITMAP_LAST_WORD_MASK(nbits)                                   \

diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index dba35e413371e599045d41134003a1ef8713fd38..66ccda9623d29b8da6d98b3a664d7284da600434 100644 (file)
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -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 +432,9 @@ static inline void node_set_offline(int nid)
        node_clear_state(nid, N_ONLINE);
        nr_online_nodes = num_node_state(N_ONLINE);
 }
+
+extern int node_random(const nodemask_t *maskp);
+
 #else
 
 static inline int node_state(int node, enum node_states state)
@@ -460,6 +465,8 @@ 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; }
 #endif
 
 #define node_online_map        node_states[N_ONLINE]

diff --git a/kernel/fork.c b/kernel/fork.c
index 17bf7c8d65114497d5cd076a850d9a013e4d4df5..4db63b018a01a2844e88fddd7784738c78ccc77b 100644 (file)
--- 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 = node_random(&p->mems_allowed);
+       p->cpuset_slab_spread_rotor = node_random(&p->mems_allowed);
+#endif
 #ifdef CONFIG_TRACE_IRQFLAGS
        p->irq_events = 0;
 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW

diff --git a/lib/bitmap.c b/lib/bitmap.c
index e3c9e999501e43f8ae0a66876c869c45bdaaf923..2f4412e4d0719c25ca1d4948d489eee8c998f444 100644 (file)
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -754,7 +754,7 @@ 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;
 

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index e7fb9d25c54eb80a62a987fbfd5cb08c4ae8e055..8b57173c1dd5b09a8bb0b3e24fedb8c8584ce447 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -93,6 +93,7 @@
 
 #include <asm/tlbflush.h>
 #include <asm/uaccess.h>
+#include <linux/random.h>
 
 #include "internal.h"
 
@@ -1645,6 +1646,21 @@ static inline unsigned interleave_nid(struct mempolicy *pol,
                return interleave_nodes(pol);
 }
 
+/*
+ * 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;
+}
+
 #ifdef CONFIG_HUGETLBFS
 /*
  * huge_zonelist(@vma, @addr, @gfp_flags, @mpol)