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SubjectRe: [PATCH incremental] cpusets: initialize spread rotor lazily
On Mon 18-04-11 13:19:09, David Rientjes wrote:
> On Mon, 18 Apr 2011, Michal Hocko wrote:
[...]
> > > 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?
> >
>
> Because lazy initialization is another feature on top of the existing
> patch so it should be done incrementally instead of proposing an entirely
> new patch which is already mostly in -mm.

ok, makes sense

> >
> > [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@suse.cz>
> > Subject: cpusets: initialize spread mem/slab rotor lazily
> >
[...]
> > Also do not use -1 for unitialized nodes and rather use NUMA_NO_NODE
> > instead.
> >
>
> Don't need to refer to a previous version that used -1 since it will never
> be committed and nobody will know what you're talking about in the git
> log.

removed

[...]
> > 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);
> > +
>
> So one function has the `=' on the line with the assignment (preferred)
> and the other has it on the new value?

fixed

Thanks! Updated patch bellow.

Changes from v3:
- code style fix
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}
---
From: Michal Hocko <mhocko@suse.cz>
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 initialize it lazily when rotors are used
for the first time.
This will also catch the case when we set up spread mem/slab later.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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 23:24:02.000000000 +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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