[PATCH] discontigmem fixes and cleanups

From Martin Bligh

This patch fixes a nasty bug that wli found in buffer.c which
cause an oops - we were using contig_page_data on a discontigmem
machine. It's a slightly modified version of the fix wli suggested,
tested on NUMA-Q.

I've also added code to not define contig_page_data for discontigmem
systems, to stop this from happening again. I wrapped a couple of
bootmem functions that were using it in #ifndef CONFIG_DISCONTIGMEM.
I suppose it's possible (though unlikely) that some other discontig
arch might need to wrap a couple of functions in their tree similarly,
but any borkage will just give a simple clear compiler error telling
them exactly where the problem is.

fs/buffer.c

@@ -462,12 +462,17 @@ void __invalidate_buffers(kdev_t dev, int destroy_dirty_buffers)
 static void free_more_memory(void)
 {
 	struct zone *zone;
+	pg_data_t *pgdat;
 
-	zone = contig_page_data.node_zonelists[GFP_NOFS&GFP_ZONEMASK].zones[0];
 	wakeup_bdflush(1024);
 	blk_run_queues();
 	yield();
-	try_to_free_pages(zone, GFP_NOFS, 0);
+
+	for_each_pgdat(pgdat) {
+		zone = pgdat->node_zonelists[GFP_NOFS&GFP_ZONEMASK].zones[0];
+		if (zone)
+			try_to_free_pages(zone, GFP_NOFS, 0);
+	}
 }
 
 /*

mm/bootmem.c

@@ -311,6 +311,7 @@ unsigned long __init free_all_bootmem_node (pg_data_t *pgdat)
 	return(free_all_bootmem_core(pgdat));
 }
 
+#ifndef CONFIG_DISCONTIGMEM
 unsigned long __init init_bootmem (unsigned long start, unsigned long pages)
 {
 	max_low_pfn = pages;
@@ -334,6 +335,7 @@ unsigned long __init free_all_bootmem (void)
 {
 	return(free_all_bootmem_core(&contig_page_data));
 }
+#endif /* !CONFIG_DISCONTIGMEM */
 
 void * __init __alloc_bootmem (unsigned long size, unsigned long align, unsigned long goal)
 {

mm/numa.c

@@ -11,11 +11,11 @@
 
 int numnodes = 1;	/* Initialized for UMA platforms */
 
+#ifndef CONFIG_DISCONTIGMEM
+
 static bootmem_data_t contig_bootmem_data;
 pg_data_t contig_page_data = { .bdata = &contig_bootmem_data };
 
-#ifndef CONFIG_DISCONTIGMEM
-
 /*
  * This is meant to be invoked by platforms whose physical memory starts
  * at a considerably higher value than 0. Examples are Super-H, ARM, m68k.