[PATCH 4/9] defrag helper functions

[Joel Schopp]

This patch contains a handful of trivial functions, and one fairly short function
that finds an unallocated 2^MAX_ORDER-1 sized block from one type and moves it
to another type.

Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
Signed-off-by: Joel Schopp <jschopp@xxxxxxxxxxxxxx>


Index: 2.6.13-joel2/mm/page_alloc.c
===================================================================
--- 2.6.13-joel2.orig/mm/page_alloc.c	2005-09-20 13:45:47.%N -0500
+++ 2.6.13-joel2/mm/page_alloc.c	2005-09-20 14:16:35.%N -0500
@@ -63,7 +63,62 @@ int sysctl_lowmem_reserve_ratio[MAX_NR_Z
 
 EXPORT_SYMBOL(totalram_pages);
 EXPORT_SYMBOL(nr_swap_pages);
+static inline int need_min_fallback_reserve(struct zone *zone)
+{
+	return (zone->free_pages >> MAX_ORDER) < zone->fallback_reserve;
+}
+static inline int is_min_fallback_reserved(struct zone *zone)
+{
+	return zone->fallback_balance < 0;
+}
+static inline unsigned int get_pageblock_type(struct zone *zone,
+					      struct page *page)
+{
+	unsigned long pfn = page_to_pfn(page);
+	int i, bitidx;
+	unsigned int type = 0;
+	unsigned long *usemap;
+
+	bitidx = pfn_to_bitidx(zone, pfn);
+	usemap = pfn_to_usemap(zone, pfn);
+
+	for (i=0; i < BITS_PER_RCLM_TYPE; i++) {
+		type = (type << 1);
+		type |= (!!test_bit(bitidx+i, usemap));
+	}
+
+	return type;
+}
 
+void assign_bit(int bit_nr, unsigned long* map, int value)
+{
+	switch (value) {
+	case 0:
+		clear_bit(bit_nr, map);
+		break;
+	default:
+		set_bit(bit_nr, map);
+	}
+}
+/*
+ * Reserve a block of pages for an allocation type & enforce function
+ * being changed if more bits are added to keep track of additional types
+ */
+BUILD_BUG_ON(BITS_PER_RCLM_TYPE > 2)
+static inline void set_pageblock_type(struct zone *zone, struct page *page,
+				      int type)
+{
+	unsigned long pfn = page_to_pfn(page);
+	int bitidx;
+	unsigned long *usemap;
+
+	usemap = pfn_to_usemap(zone, pfn);
+	bitidx = pfn_to_bitidx(zone, pfn);
+
+	assign_bit(bitidx, usemap, (type & 0x1));
+	assign_bit(bitidx + 1, usemap, (type & 0x2));
+
+}
 /*
  * Used by page_zone() to look up the address of the struct zone whose
  * id is encoded in the upper bits of page->flags
@@ -465,6 +520,41 @@ static void prep_new_page(struct page *p
 	kernel_map_pages(page, 1 << order, 1);
 }
 
+/*
+ * Find a list that has a 2^MAX_ORDER-1 block of pages available and
+ * return it
+ */
+static inline struct page* steal_largepage(struct zone *zone, int alloctype)
+{
+	struct page *page;
+	struct free_area *area;
+	int i=0;
+
+	for(i = 0; i < RCLM_TYPES; i++) {
+		if(i == alloctype)
+			continue;
+
+		area = &zone->free_area_lists[i][MAX_ORDER-1];
+		if(!list_empty(&area->free_list))
+			break;
+	}
+	if (i == RCLM_TYPES) return NULL;
+
+	page = list_entry(area->free_list.next, struct page, lru);
+	area->nr_free--;
+
+	if (!is_min_fallback_reserved(zone) &&
+	    need_min_fallback_reserve(zone)) {
+		alloctype = RCLM_FALLBACK;
+	}
+
+	set_pageblock_type(zone, page, alloctype);
+	dec_reserve_count(zone, i);
+	inc_reserve_count(zone, alloctype);
+
+	return page;
+}
+
 /* 
  * Do the hard work of removing an element from the buddy allocator.
  * Call me with the zone->lock already held.