Re: [PATCH 6/6] Use one zonelist that is filtered by nodemask

[Mel Gorman <mel@csn.ul.ie>]

On (09/11/07 07:45), Christoph Lameter didst pronounce:
> On Fri, 9 Nov 2007, Mel Gorman wrote:
> 
> >  struct page * fastcall
> >  __alloc_pages(gfp_t gfp_mask, unsigned int order,
> >  		struct zonelist *zonelist)
> >  {
> > +	/*
> > +	 * Use a temporary nodemask for __GFP_THISNODE allocations. If the
> > +	 * cost of allocating on the stack or the stack usage becomes
> > +	 * noticable, allocate the nodemasks per node at boot or compile time
> > +	 */
> > +	if (unlikely(gfp_mask & __GFP_THISNODE)) {
> > +		nodemask_t nodemask;
> 
> Hmmm.. This places a potentially big structure on the stack. nodemask can 
> contain up to 1024 bits which means 128 bytes. Maybe keep an array of 
> gfp_thisnode nodemasks (node_nodemask?) and use node_nodemask[nid]?

Went back and revisited this. Allocating them at boot-time is below but
essentially it is a silly and it makes sense to just have two zonelists
where one of them is for __GFP_THISNODE. Implementation wise, this involves
dropping the last patch in the set and the overall result is still a reduction
in the number of zonelists.

diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.24-rc2-mm1-040_use_one_zonelist/include/linux/gfp.h linux-2.6.24-rc2-mm1-045_use_static_nodemask/include/linux/gfp.h
--- linux-2.6.24-rc2-mm1-040_use_one_zonelist/include/linux/gfp.h	2007-11-19 19:27:15.000000000 +0000
+++ linux-2.6.24-rc2-mm1-045_use_static_nodemask/include/linux/gfp.h	2007-11-19 19:28:55.000000000 +0000
@@ -175,7 +175,6 @@ FASTCALL(__alloc_pages(gfp_t, unsigned i
 extern struct page *
 FASTCALL(__alloc_pages_nodemask(gfp_t, unsigned int,
 				struct zonelist *, nodemask_t *nodemask));
-extern nodemask_t *nodemask_thisnode(int nid, nodemask_t *nodemask);
 
 static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
 						unsigned int order)
@@ -187,13 +186,10 @@ static inline struct page *alloc_pages_n
 	if (nid < 0)
 		nid = numa_node_id();
 
-	/* Use a temporary nodemask for __GFP_THISNODE allocations */
 	if (unlikely(gfp_mask & __GFP_THISNODE)) {
-		nodemask_t nodemask;
-
 		return __alloc_pages_nodemask(gfp_mask, order,
 				node_zonelist(nid),
-				nodemask_thisnode(nid, &nodemask));
+				NODE_DATA(nid)->nodemask_thisnode);
 	}
 
 	return __alloc_pages(gfp_mask, order, node_zonelist(nid));
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.24-rc2-mm1-040_use_one_zonelist/include/linux/mmzone.h linux-2.6.24-rc2-mm1-045_use_static_nodemask/include/linux/mmzone.h
--- linux-2.6.24-rc2-mm1-040_use_one_zonelist/include/linux/mmzone.h	2007-11-19 19:27:15.000000000 +0000
+++ linux-2.6.24-rc2-mm1-045_use_static_nodemask/include/linux/mmzone.h	2007-11-19 19:28:55.000000000 +0000
@@ -519,6 +519,9 @@ typedef struct pglist_data {
 	struct zone node_zones[MAX_NR_ZONES];
 	struct zonelist node_zonelist;
 	int nr_zones;
+
+	/* nodemask suitable for __GFP_THISNODE */
+	nodemask_t *nodemask_thisnode;
 #ifdef CONFIG_FLAT_NODE_MEM_MAP
 	struct page *node_mem_map;
 #endif
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.24-rc2-mm1-040_use_one_zonelist/mm/page_alloc.c linux-2.6.24-rc2-mm1-045_use_static_nodemask/mm/page_alloc.c
--- linux-2.6.24-rc2-mm1-040_use_one_zonelist/mm/page_alloc.c	2007-11-19 19:27:15.000000000 +0000
+++ linux-2.6.24-rc2-mm1-045_use_static_nodemask/mm/page_alloc.c	2007-11-19 19:28:55.000000000 +0000
@@ -1695,28 +1695,36 @@ got_pg:
 }
 
 /* Creates a nodemask suitable for GFP_THISNODE allocations */
-nodemask_t *nodemask_thisnode(int nid, nodemask_t *nodemask)
+static inline void alloc_node_nodemask_thisnode(pg_data_t *pgdat)
 {
-	nodes_clear(*nodemask);
-	node_set(nid, *nodemask);
+	nodemask_t *nodemask_thisnode;
 
-	return nodemask;
+	/* Only a machine with multiple nodes needs the nodemask */
+	if (!NUMA_BUILD || num_online_nodes() == 1)
+		return;
+	
+	/* Allocate the nodemask. Serious if it fails, but not world ending */
+	nodemask_thisnode = alloc_bootmem_node(pgdat, sizeof(nodemask_t));
+	if (!nodemask_thisnode) {
+		printk(KERN_WARNING
+			"thisnode nodemask allocation failed."
+			"There may be sub-optimal NUMA placement.\n");
+		return;
+	}
+
+	/* Initialise the nodemask to only cover the current node */
+	nodes_clear(*nodemask_thisnode);
+	node_set(pgdat->node_id, *nodemask_thisnode);
+	pgdat->nodemask_thisnode = nodemask_thisnode;
 }
 
 struct page * fastcall
 __alloc_pages(gfp_t gfp_mask, unsigned int order,
 		struct zonelist *zonelist)
 {
-	/*
-	 * Use a temporary nodemask for __GFP_THISNODE allocations. If the
-	 * cost of allocating on the stack or the stack usage becomes
-	 * noticable, allocate the nodemasks per node at boot or compile time
-	 */
 	if (unlikely(gfp_mask & __GFP_THISNODE)) {
-		nodemask_t nodemask;
-
-		return __alloc_pages_internal(gfp_mask, order,
-			zonelist, nodemask_thisnode(numa_node_id(), &nodemask));
+		return __alloc_pages_internal(gfp_mask, order, zonelist,
+			NODE_DATA(numa_node_id())->nodemask_thisnode);
 	}
 
 	return __alloc_pages_internal(gfp_mask, order, zonelist, NULL);
@@ -3501,6 +3509,7 @@ void __meminit free_area_init_node(int n
 	calculate_node_totalpages(pgdat, zones_size, zholes_size);
 
 	alloc_node_mem_map(pgdat);
+	alloc_node_nodemask_thisnode(pgdat);
 
 	free_area_init_core(pgdat, zones_size, zholes_size);
 }

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