linux-kernel - Re: [PATCH 5/6] Filter based on a nodemask as well as a gfp

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Message-ID: <20070821091202.GE29794@skynet.ie>
Date:	Tue, 21 Aug 2007 10:12:02 +0100
From:	mel@...net.ie (Mel Gorman)
To:	Christoph Lameter <clameter@....com>
Cc:	Lee.Schermerhorn@...com, ak@...e.de, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 5/6] Filter based on a nodemask as well as a gfp_mask

On (17/08/07 14:29), Christoph Lameter didst pronounce:
> On Fri, 17 Aug 2007, Mel Gorman wrote:
> 
> > @@ -696,6 +696,16 @@ static inline struct zonelist *node_zone
> >  	return &NODE_DATA(nid)->node_zonelist;
> >  }
> >  
> > +static inline int zone_in_nodemask(unsigned long zone_addr,
> > +				nodemask_t *nodes)
> > +{
> > +#ifdef CONFIG_NUMA
> > +	return node_isset(zonelist_zone(zone_addr)->node, *nodes);
> > +#else
> > +	return 1;
> > +#endif /* CONFIG_NUMA */
> > +}
> > +
> 
> This is dereferencind the zone in a filtering operation. I wonder if
> we could encode the node in the zone_addr as well? x86_64 aligns zones on
> page boundaries. So we have 10 bits left after taking 2 for the zone id.
> 

I had considered it but not gotten around to an implementation. A quick
look shows that it is likely to be a win on x86_64 and ppc64 as in those
places NODES_SHIFT is small enough to fit into the lower bits of the
zone addresses. It does not appear to be the case on IA-64 though. The
INTERNODE_CACHE_SHIFT will be around 7 but the NODES_SHIFT defaults to
10 so it will not fit.

I'll try it out anyway.

> > -int cpuset_zonelist_valid_mems_allowed(struct zonelist *zl)
> > +int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
> >  {
> > -	int i;
> > -
> > -	for (i = 0; zl->_zones[i]; i++) {
> > -		int nid = zone_to_nid(zonelist_zone(zl->_zones[i]));
> > +	int nid;
> >  
> > +	for_each_node_mask(nid, *nodemask)
> >  		if (node_isset(nid, current->mems_allowed))
> >  			return 1;
> > -	}
> > +
> >  	return 0;
> 
> Hmmm... This is equivalent to
> 
> nodemask_t temp;
> 
> nodes_and(temp, nodemask, current->mems_allowed);
> return !nodes_empty(temp);
> 
> which avoids the loop over all nodes.
> 

Good point. I've replaced the code with your version.

> > -	}
> > -	if (num == 0) {
> > -		kfree(zl);
> > -		return ERR_PTR(-EINVAL);
> > +	for_each_node_mask(nd, *nodemask) {
> > +		struct zone *z = &NODE_DATA(nd)->node_zones[k];
> > +		if (z->present_pages > 0)
> > +			return 1;
> 
> Here you could use an and with the N_HIGH_MEMORY or N_NORMAL_MEMORY 
> nodemask.
> 

I'm basing against 2.6.23-rc3 at the moment. I'll add an additional
patch later to use the N_HIGH_MEMORy and N_NORMAL_MEMORY nodemasks.

> > @@ -1149,12 +1125,19 @@ unsigned slab_node(struct mempolicy *pol
> >  	case MPOL_INTERLEAVE:
> >  		return interleave_nodes(policy);
> >  
> > -	case MPOL_BIND:
> > +	case MPOL_BIND: {
> 
> No { } needed.
> 
> >  		/*
> >  		 * Follow bind policy behavior and start allocation at the
> >  		 * first node.
> >  		 */
> > -		return zone_to_nid(zonelist_zone(policy->v.zonelist->_zones[0]));
> > +		struct zonelist *zonelist;
> > +		unsigned long *z;

Without the {}, it would fail to compile here

> > +		enum zone_type highest_zoneidx = gfp_zone(GFP_KERNEL);
> > +		zonelist = &NODE_DATA(numa_node_id())->node_zonelist;
> > +		z = first_zones_zonelist(zonelist, &policy->v.nodes,
> > +							highest_zoneidx);
> > +		return zone_to_nid(zonelist_zone(*z));
> > +	}
> >  
> >  	case MPOL_PREFERRED:
> >  		if (policy->v.preferred_node >= 0)
> 
> > @@ -1330,14 +1314,6 @@ struct mempolicy *__mpol_copy(struct mem
> >  	}
> >  	*new = *old;
> >  	atomic_set(&new->refcnt, 1);
> > -	if (new->policy == MPOL_BIND) {
> > -		int sz = ksize(old->v.zonelist);
> > -		new->v.zonelist = kmemdup(old->v.zonelist, sz, GFP_KERNEL);
> > -		if (!new->v.zonelist) {
> > -			kmem_cache_free(policy_cache, new);
> > -			return ERR_PTR(-ENOMEM);
> > -		}
> > -	}
> >  	return new;
> 
> That is a good optimization.
> 

Thanks

> > @@ -1680,32 +1647,6 @@ void mpol_rebind_policy(struct mempolicy
> >  						*mpolmask, *newmask);
> >  		*mpolmask = *newmask;
> >  		break;
> > -	case MPOL_BIND: {
> > -		nodemask_t nodes;
> > -		unsigned long *z;
> > -		struct zonelist *zonelist;
> > -
> > -		nodes_clear(nodes);
> > -		for (z = pol->v.zonelist->_zones; *z; z++)
> > -			node_set(zone_to_nid(zonelist_zone(*z)), nodes);
> > -		nodes_remap(tmp, nodes, *mpolmask, *newmask);
> > -		nodes = tmp;
> > -
> > -		zonelist = bind_zonelist(&nodes);
> > -
> > -		/* If no mem, then zonelist is NULL and we keep old zonelist.
> > -		 * If that old zonelist has no remaining mems_allowed nodes,
> > -		 * then zonelist_policy() will "FALL THROUGH" to MPOL_DEFAULT.
> > -		 */
> > -
> > -		if (!IS_ERR(zonelist)) {
> > -			/* Good - got mem - substitute new zonelist */
> > -			kfree(pol->v.zonelist);
> > -			pol->v.zonelist = zonelist;
> > -		}
> > -		*mpolmask = *newmask;
> > -		break;
> > -	}
> 
> Simply dropped? We still need to recalculate the node_mask depending on 
> the new cpuset environment!
> 

It's not simply dropped. The previous patch chunk made the MPOL_BIND case
falls through to take the same action as MPOL_INTERLEAVE. Is that wrong?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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