Re: NUMA policy issues with ZONE_MOVABLE

[Christoph Lameter <clameter@sgi.com>]

On Fri, 27 Jul 2007, Mel Gorman wrote:

> This was fairly straight-forward but I wouldn't call it a bug fix for 2.6.23
> for the policys + ZONE_MOVABLE issue; I still prefer the last patch for
> the fix.
> 
> This patch uses one zonelist per node and filters based on a gfp_mask where
> necessary. It consumes less memory and reduces cache pressure at the cost
> of CPU. It also adds a zone_id field to struct zone as zone_idx is used more
> than it was previously.
> 
> Performance differences on kernbench for Total CPU time ranged from
> -0.06% to +1.19%.

Performance is equal otherwise?
 
> Obvious things that are outstanding;
> 
> o Compile-test parisc
> o Split patch in two to keep the zone_idx changes separetly
> o Verify zlccache is not broken
> o Have a version of __alloc_pages take a nodemask and ditch
>   bind_zonelist()

Yeah. I think the NUMA folks would love this but the rest of the 
developers may object.

> I can work on bringing this up to scratch during the cycle.
> 
> Patch as follows. Comments?

Glad to see some movement in this area. 

> index bc68dd9..f2a597e 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -116,6 +116,13 @@ static inline enum zone_type gfp_zone(gfp_t flags)
>  	return ZONE_NORMAL;
>  }
>  
> +static inline int should_filter_zone(struct zone *zone, int highest_zoneidx)
> +{
> +	if (zone_idx(zone) > highest_zoneidx)
> +		return 1;
> +	return 0;
> +}
> +

I think this should_filter() creates more overhead than which it saves. In 
particular true for configurations with a small number of zones like SMP 
systems. For large NUMA systems the cache savings will likely may it 
beneficial.

Simply filter all.

> @@ -258,7 +258,7 @@ static inline void mpol_fix_fork_child_flag(struct task_struct *p)
>  static inline struct zonelist *huge_zonelist(struct vm_area_struct *vma,
>  		unsigned long addr, gfp_t gfp_flags)
>  {
> -	return NODE_DATA(0)->node_zonelists + gfp_zone(gfp_flags);
> +	return &NODE_DATA(0)->node_zonelist;
>  }

These modifications look good in terrms of code size reduction.

> @@ -438,7 +439,7 @@ extern struct page *mem_map;
>  struct bootmem_data;
>  typedef struct pglist_data {
>  	struct zone node_zones[MAX_NR_ZONES];
> -	struct zonelist node_zonelists[MAX_NR_ZONES];
> +	struct zonelist node_zonelist;

Looks like a significant memory savings on 1024 node numa. zonelist has
#define MAX_ZONES_PER_ZONELIST (MAX_NUMNODES * MAX_NR_ZONES)
zones.

> @@ -185,11 +186,15 @@ static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
>  		if (NODE_DATA(node)->node_present_pages)
>  			node_set(node, nodes);
>  
> -	for (z = zonelist->zones; *z; z++)
> +	for (z = zonelist->zones; *z; z++) {
> +
> +		if (should_filter_zone(*z, highest_zoneidx))
> +			continue;

Huh? Why do you need it here? Note that this code is also going away with 
the memoryless node patch. We can use the nodes with memory nodemask here.

> diff --git a/mm/slub.c b/mm/slub.c
> index 9b2d617..a020a12 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1276,6 +1276,7 @@ static struct page *get_any_partial(struct kmem_cache *s, gfp_t flags)
>  	struct zonelist *zonelist;
>  	struct zone **z;
>  	struct page *page;
> +	enum zone_type highest_zoneidx = gfp_zone(flags);
>  
>  	/*
>  	 * The defrag ratio allows a configuration of the tradeoffs between
> @@ -1298,11 +1299,13 @@ static struct page *get_any_partial(struct kmem_cache *s, gfp_t flags)
>  	if (!s->defrag_ratio || get_cycles() % 1024 > s->defrag_ratio)
>  		return NULL;
>  
> -	zonelist = &NODE_DATA(slab_node(current->mempolicy))
> -					->node_zonelists[gfp_zone(flags)];
> +	zonelist = &NODE_DATA(slab_node(current->mempolicy))->node_zonelist;
>  	for (z = zonelist->zones; *z; z++) {
>  		struct kmem_cache_node *n;
>  
> +		if (should_filter_zone(*z, highest_zoneidx))
> +			continue;
> +
>  		n = get_node(s, zone_to_nid(*z));
>  
>  		if (n && cpuset_zone_allowed_hardwall(*z, flags) &&

Isnt there some way to fold these traversals into a common page allocator 
function?

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