[PATCH incremental] cpusets: initialize spread rotor lazily

[Michal Hocko]

On Fri 15-04-11 16:42:13, David Rientjes wrote:
> On Fri, 15 Apr 2011, Michal Hocko wrote:
> 
> > You are right. I was thinking about lazy approach and initialize those
> > values when they are used for the first time. What about the patch
> > below?
> > 
> > Change from v1:
> > - initialize cpuset_{mem,slab}_spread_rotor lazily
> > 
> 
> The difference between this v2 patch and what is already in the -mm tree 
> (http://userweb.kernel.org/~akpm/mmotm/broken-out/cpusets-randomize-node-rotor-used-in-cpuset_mem_spread_node.patch) 
> is the lazy initialization by adding cpuset_{mem,slab}_spread_node()?

Yes.
 
> It'd probably be better to just make an incremental patch on top of 
> mmotm-2011-04-14-15-08 with a new changelog and then propose with with 
> your list of reviewed-by lines.

Sure, no problems. Maybe it will be easier for Andrew as well.

> 
> Andrew could easily drop the earlier version and merge this v2, but I'm 
> asking for selfish reasons:

Just out of curiosity. What is the reason? Don't want to wait for new mmotm?

> please use NUMA_NO_NODE instead of -1.

Good idea. I have updated the patch.

Changes from v2:
 - use NUMA_NO_NODE rather than hardcoded -1
 - make the patch incremental to the original one because that one is in
   -mm tree already.
Changes from v1:
 - initialize cpuset_{mem,slab}_spread_rotor lazily}

[Here is the follow-up patch based on top of
http://userweb.kernel.org/~akpm/mmotm/broken-out/cpusets-randomize-node-rotor-used-in-cpuset_mem_spread_node.patch]
---
From: Michal Hocko <mhocko@xxxxxxx>
Subject: cpusets: initialize spread mem/slab rotor lazily

Kosaki Motohiro raised a concern that copy_process is hot path and we do
not want to initialize cpuset_{mem,slab}_spread_rotor if they are not
used most of the time.

I think that we should rather intialize it lazily when rotors are used
for the first time.
This will also catch the case when we set up spread mem/slab later.

Also do not use -1 for unitialized nodes and rather use NUMA_NO_NODE
instead.

Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
---
 cpuset.c |    8 ++++++++
 fork.c   |    4 ++--
 2 files changed, 10 insertions(+), 2 deletions(-)
Index: linus_tree/kernel/cpuset.c
===================================================================
--- linus_tree.orig/kernel/cpuset.c	2011-04-18 10:33:15.000000000 +0200
+++ linus_tree/kernel/cpuset.c	2011-04-18 10:33:56.000000000 +0200
@@ -2460,11 +2460,19 @@ static int cpuset_spread_node(int *rotor
 
 int cpuset_mem_spread_node(void)
 {
+	if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
+		current->cpuset_mem_spread_rotor =
+			node_random(&current->mems_allowed);
+
 	return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
 }
 
 int cpuset_slab_spread_node(void)
 {
+	if (current->cpuset_slab_spread_rotor == NUMA_NO_NODE)
+		current->cpuset_slab_spread_rotor
+			= node_random(&current->mems_allowed);
+
 	return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
 }
 
Index: linus_tree/kernel/fork.c
===================================================================
--- linus_tree.orig/kernel/fork.c	2011-04-18 10:33:15.000000000 +0200
+++ linus_tree/kernel/fork.c	2011-04-18 10:33:56.000000000 +0200
@@ -1126,8 +1126,8 @@ 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);
+	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
+	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
 #endif
 #ifdef CONFIG_TRACE_IRQFLAGS
 	p->irq_events = 0;
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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