[RFC] mbind: Restrict nodes to the currently allowed cpuset

[RFC] mbind: Restrict nodes to the currently allowed cpuset

[Christoph Lameter]

Currently one can specify an arbitrary node mask to mbind that includes nodes
not allowed. If that is done with an interleave policy then we will go around
all the nodes. Those outside of the currently allowed cpuset will be redirected
to the border nodes. Interleave will then create imbalances at the borders
of the cpuset.

This patch restricts the nodes to the currently allowed cpuset.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

----

I still wonder if this is the right approach. Could mbind be used to set 
up policies that are larger than the existing cpuset? Or could mbind be 
used to set up a policy and then the cpuset would change?



Index: linux-2.6.19-mm1/mm/mempolicy.c
===================================================================
--- linux-2.6.19-mm1.orig/mm/mempolicy.c	2006-12-11 19:00:38.224610647 -0800
+++ linux-2.6.19-mm1/mm/mempolicy.c	2006-12-13 11:13:10.175294067 -0800
@@ -882,6 +882,7 @@ asmlinkage long sys_mbind(unsigned long 
 	int err;
 
 	err = get_nodes(&nodes, nmask, maxnode);
+	nodes_and(nodes, nodes, current->mems_allowed);
 	if (err)
 		return err;
 	return do_mbind(start, len, mode, &nodes, flags);

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Re: [RFC] mbind: Restrict nodes to the currently allowed cpuset

[Paul Jackson]

Christoph wrote:
> Could mbind be used to set 
> up policies that are larger than the existing cpuset? Or could mbind be 
> used to set up a policy and then the cpuset would change?

My intention (hopefully the code matches this) is that mbind nodes are
constrained to fit in the cpuset.  If you ask to mbind more nodes, those
outside the cpuset are masked off.  If you later change the cpuset, then
we mask more nodes off to continue to fit in the cpuset.  If this gets us
down to an empty mbind list, then you get to use whatever memory nodes are
in your new cpuset.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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Re: [RFC] mbind: Restrict nodes to the currently allowed cpuset

[Andi Kleen]

On Thursday 04 January 2007 20:16, Christoph Lameter wrote:
> Currently one can specify an arbitrary node mask to mbind that includes nodes
> not allowed. If that is done with an interleave policy then we will go around
> all the nodes. Those outside of the currently allowed cpuset will be redirected
> to the border nodes. Interleave will then create imbalances at the borders
> of the cpuset.
> 
> This patch restricts the nodes to the currently allowed cpuset.

Fine by me.

-Andi

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