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Date: Thu, 29 Apr 2010 15:09:51 -0500
From: Jack Steiner <steiner@....com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] - 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.
NOTE: this patch is on TOP of the previous patch:
[PATCH] - New round-robin rotor for SLAB allocations
http://marc.info/?l=linux-mm&m=127231565321947&w=2
Signed-off-by: Jack Steiner <steiner@....com>
---
V2 - initial patch was generated against the wrong tree. This patch is based
on linux-next.
V3 - Eliminate new function bitmap_find_nth_bit(). Rename bitmap_ord_to_pos()
and export it.
arch/x86/mm/numa.c | 17 +++++++++++++++++
include/linux/bitmap.h | 1 +
include/linux/nodemask.h | 5 +++++
kernel/fork.c | 4 ++++
lib/bitmap.c | 2 +-
5 files changed, 28 insertions(+), 1 deletion(-)
Index: linux/arch/x86/mm/numa.c
===================================================================
--- linux.orig/arch/x86/mm/numa.c 2010-04-28 09:59:10.158899192 -0500
+++ linux/arch/x86/mm/numa.c 2010-04-29 13:53:48.531783017 -0500
@@ -2,6 +2,7 @@
#include <linux/topology.h>
#include <linux/module.h>
#include <linux/bootmem.h>
+#include <linux/random.h>
#ifdef CONFIG_DEBUG_PER_CPU_MAPS
# define DBG(x...) printk(KERN_DEBUG x)
@@ -65,3 +66,19 @@ const struct cpumask *cpumask_of_node(in
}
EXPORT_SYMBOL(cpumask_of_node);
#endif
+
+/*
+ * 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;
+}
+EXPORT_SYMBOL(__node_random);
Index: linux/include/linux/bitmap.h
===================================================================
--- linux.orig/include/linux/bitmap.h 2010-04-28 09:59:10.158899192 -0500
+++ linux/include/linux/bitmap.h 2010-04-29 13:54:04.639408240 -0500
@@ -141,6 +141,7 @@ extern int bitmap_find_free_region(unsig
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) \
( \
Index: linux/include/linux/nodemask.h
===================================================================
--- linux.orig/include/linux/nodemask.h 2010-04-28 09:59:10.158899192 -0500
+++ linux/include/linux/nodemask.h 2010-04-28 10:01:42.878971800 -0500
@@ -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?
*
@@ -267,6 +269,9 @@ static inline int __first_unset_node(con
find_first_zero_bit(maskp->bits, MAX_NUMNODES));
}
+#define node_random(mask) __node_random(&(mask))
+extern int __node_random(const nodemask_t *maskp);
+
#define NODE_MASK_LAST_WORD BITMAP_LAST_WORD_MASK(MAX_NUMNODES)
#if MAX_NUMNODES <= BITS_PER_LONG
Index: linux/kernel/fork.c
===================================================================
--- linux.orig/kernel/fork.c 2010-04-28 09:59:10.158899192 -0500
+++ linux/kernel/fork.c 2010-04-28 10:03:11.580014823 -0500
@@ -1079,6 +1079,10 @@ static struct task_struct *copy_process(
}
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
Index: linux/lib/bitmap.c
===================================================================
--- linux.orig/lib/bitmap.c 2010-04-28 09:59:10.158899192 -0500
+++ linux/lib/bitmap.c 2010-04-29 13:53:28.270906295 -0500
@@ -672,7 +672,7 @@ static int bitmap_pos_to_ord(const unsig
*
* 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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