linux-kernel - Re: [2.6.24 regression][BUGFIX] numactl --interleave=all doesn't works on memoryless node.

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Date:	Wed, 06 Feb 2008 11:11:21 -0500
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	Paul Jackson <pj@....com>, Mel Gorman <mel@....ul.ie>,
	torvalds@...ux-foundation.org, Eric Whitney <eric.whitney@...com>
Subject: Re: [2.6.24 regression][BUGFIX] numactl --interleave=all doesn't
	works on memoryless node.

On Tue, 2008-02-05 at 18:17 -0800, David Rientjes wrote:
> On Tue, 5 Feb 2008, Lee Schermerhorn wrote:
> 
> > Index: Linux/mm/mempolicy.c
> > ===================================================================
> > --- Linux.orig/mm/mempolicy.c	2008-02-05 11:25:17.000000000 -0500
> > +++ Linux/mm/mempolicy.c	2008-02-05 16:03:11.000000000 -0500
> > @@ -131,7 +131,7 @@ static int mpol_check_policy(int mode, n
> >  			return -EINVAL;
> >  		break;
> >  	}
> > - 	return nodes_subset(*nodes, node_states[N_HIGH_MEMORY]) ? 0 : -EINVAL;
> > + 	return 0;
> >  }
> >  
> >  /* Generate a custom zonelist for the BIND policy. */
> 
> This change will be necessary when the nodemask passed from the syscall is 
> saved in the struct mempolicy as the intent of the application as well.
> 
> > @@ -188,8 +188,6 @@ static struct mempolicy *mpol_new(int mo
> >  	switch (mode) {
> >  	case MPOL_INTERLEAVE:
> >  		policy->v.nodes = *nodes;
> > -		nodes_and(policy->v.nodes, policy->v.nodes,
> > -					node_states[N_HIGH_MEMORY]);
> >  		if (nodes_weight(policy->v.nodes) == 0) {
> >  			kmem_cache_free(policy_cache, policy);
> >  			return ERR_PTR(-EINVAL);
> > @@ -426,9 +424,13 @@ static int contextualize_policy(int mode
> >  	if (!nodes)
> >  		return 0;
> >  
> > +	/*
> > +	 * Restrict the nodes to the allowed nodes in the cpuset.
> > +	 * This is guaranteed to be a subset of nodes with memory.
> > +	 */
> >  	cpuset_update_task_memory_state();
> > -	if (!cpuset_nodes_subset_current_mems_allowed(*nodes))
> > -		return -EINVAL;
> > +	nodes_and(*nodes, *nodes, cpuset_current_mems_allowed);
> > +
> >  	return mpol_check_policy(mode, nodes);
> >  }
> >  
> 
> I would defer the intersection until later because contextualize_policy() 
> is called before mpol_new() so we have no struct mempolicy to save the 
> intent in.  It doesn't matter for the sake of this change, I know, but you 
> could move this intersection to mpol_new() and give us an opportunity to 
> store the user's nodemask in the mempolicy with a one-line change and get 
> the same desired result.

Hi, David:

I wanted to avoid a major restructuring of the code for this patch.
However, now that both do_mbind() and do_set_mempolicy() both call
contextualize_policy() [which calls mpol_check_policy()] immediately
before calling mpol_new(), I agree we can push this "contextualization"
down there.  I would like to defer this to another patch--perhaps as
part of Paul's rework of mempolicy and cpusets.  

Note that there is another caller of mpol_new() --
mpol_shared_policy_init().  We'll need to decide whether that call needs
to be contextualized, as it constructs a policy from the tmpfs or
hugetlbfs superblock, as specified on the mount command [or kernel
command line?].  As this is a privileged operation, one could argue that
it should be exempt from cpuset constraints.

> 
> You can now remove cpuset_nodes_subset_current_mems_allowed() from 
> linux/cpuset.h.
> 
> > @@ -797,7 +799,7 @@ static long do_mbind(unsigned long start
> >  	if (end == start)
> >  		return 0;
> >  
> > -	if (mpol_check_policy(mode, nmask))
> > +	if (contextualize_policy(mode, nmask))
> >  		return -EINVAL;
> >  
> >  	new = mpol_new(mode, nmask);
> > @@ -915,10 +917,6 @@ asmlinkage long sys_mbind(unsigned long 
> >  	err = get_nodes(&nodes, nmask, maxnode);
> >  	if (err)
> >  		return err;
> > -#ifdef CONFIG_CPUSETS
> > -	/* Restrict the nodes to the allowed nodes in the cpuset */
> > -	nodes_and(nodes, nodes, current->mems_allowed);
> > -#endif
> >  	return do_mbind(start, len, mode, &nodes, flags);
> >  }
> >  
> 
> Looks good, thanks for doing this.

As I mentioned to Christoph, I'll post a new version that I think
handles the error conditions better.

Later,
Lee

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