Index: linux-2.6.15-rc3/include/linux/mmzone.h
===================================================================
--- linux-2.6.15-rc3.orig/include/linux/mmzone.h	2005-11-29 03:51:27.000000000 +0000
+++ linux-2.6.15-rc3/include/linux/mmzone.h	2005-11-30 00:35:48.000000000 +0000
@@ -122,6 +122,7 @@ struct zone {
 	unsigned long		lowmem_reserve[MAX_NR_ZONES];
 
 #ifdef CONFIG_NUMA
+	atomic_t		pages_unmapped;		/* Unmapped pagecache pages */
 	struct per_cpu_pageset	*pageset[NR_CPUS];
 #else
 	struct per_cpu_pageset	pageset[NR_CPUS];
Index: linux-2.6.15-rc3/include/linux/rmap.h
===================================================================
--- linux-2.6.15-rc3.orig/include/linux/rmap.h	2005-11-29 03:51:27.000000000 +0000
+++ linux-2.6.15-rc3/include/linux/rmap.h	2005-11-30 00:48:06.000000000 +0000
@@ -71,8 +71,8 @@ void __anon_vma_link(struct vm_area_stru
  * rmap interfaces called when adding or removing pte of page
  */
 void page_add_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
-void page_add_file_rmap(struct page *);
-void page_remove_rmap(struct page *);
+int page_add_file_rmap(struct page *);
+int page_remove_rmap(struct page *);
 
 /**
  * page_dup_rmap - duplicate pte mapping to a page
Index: linux-2.6.15-rc3/mm/fremap.c
===================================================================
--- linux-2.6.15-rc3.orig/mm/fremap.c	2005-11-29 03:51:27.000000000 +0000
+++ linux-2.6.15-rc3/mm/fremap.c	2005-11-30 00:59:41.000000000 +0000
@@ -90,7 +90,8 @@ int install_page(struct mm_struct *mm, s
 
 	flush_icache_page(vma, page);
 	set_pte_at(mm, addr, pte, mk_pte(page, prot));
-	page_add_file_rmap(page);
+	if (page_add_file_rmap(page))
+		atomic_dec(&page_zone(page)->pages_unmapped);
 	pte_val = *pte;
 	update_mmu_cache(vma, addr, pte_val);
 	err = 0;
Index: linux-2.6.15-rc3/mm/memory.c
===================================================================
--- linux-2.6.15-rc3.orig/mm/memory.c	2005-11-29 03:51:27.000000000 +0000
+++ linux-2.6.15-rc3/mm/memory.c	2005-11-30 01:40:35.000000000 +0000
@@ -640,16 +640,18 @@ static unsigned long zap_pte_range(struc
 						addr) != page->index)
 				set_pte_at(mm, addr, pte,
 					   pgoff_to_pte(page->index));
-			if (PageAnon(page))
+			if (PageAnon(page)) {
 				anon_rss--;
-			else {
+				page_remove_rmap(page);
+			} else {
 				if (pte_dirty(ptent))
 					set_page_dirty(page);
 				if (pte_young(ptent))
 					mark_page_accessed(page);
 				file_rss--;
+				if (page_remove_rmap(page))
+					atomic_inc(&page_zone(page)->pages_unmapped);
 			}
-			page_remove_rmap(page);
 			tlb_remove_page(tlb, page);
 			continue;
 		}
@@ -1382,10 +1384,13 @@ gotten:
 	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
 	if (likely(pte_same(*page_table, orig_pte))) {
 		if (old_page) {
-			page_remove_rmap(old_page);
+			int last = page_remove_rmap(old_page);
+
 			if (!PageAnon(old_page)) {
 				dec_mm_counter(mm, file_rss);
 				inc_mm_counter(mm, anon_rss);
+				if (last)
+					atomic_inc(&page_zone(old_page)->pages_unmapped);
 			}
 		} else
 			inc_mm_counter(mm, anon_rss);
@@ -1985,7 +1990,8 @@ retry:
 			page_add_anon_rmap(new_page, vma, address);
 		} else {
 			inc_mm_counter(mm, file_rss);
-			page_add_file_rmap(new_page);
+			if (page_add_file_rmap(new_page))
+				atomic_dec(&page_zone(new_page)->pages_unmapped);
 		}
 	} else {
 		/* One of our sibling threads was faster, back out. */
Index: linux-2.6.15-rc3/mm/page_alloc.c
===================================================================
--- linux-2.6.15-rc3.orig/mm/page_alloc.c	2005-11-29 03:51:27.000000000 +0000
+++ linux-2.6.15-rc3/mm/page_alloc.c	2005-11-30 02:35:13.000000000 +0000
@@ -1844,6 +1844,7 @@ static int __devinit process_zones(int c
 			goto bad;
 
 		setup_pageset(zone->pageset[cpu], zone_batchsize(zone));
+		atomic_set(&zone->pages_unmapped, 0);
 	}
 
 	return 0;
Index: linux-2.6.15-rc3/mm/rmap.c
===================================================================
--- linux-2.6.15-rc3.orig/mm/rmap.c	2005-11-30 00:42:55.000000000 +0000
+++ linux-2.6.15-rc3/mm/rmap.c	2005-11-30 01:16:52.000000000 +0000
@@ -464,14 +464,19 @@ void page_add_anon_rmap(struct page *pag
  * @page: the page to add the mapping to
  *
  * The caller needs to hold the pte lock.
+ *
+ * Return 1 if a page changed from unmapped to mapped
  */
-void page_add_file_rmap(struct page *page)
+int page_add_file_rmap(struct page *page)
 {
 	BUG_ON(PageAnon(page));
 	BUG_ON(!pfn_valid(page_to_pfn(page)));
 
-	if (atomic_inc_and_test(&page->_mapcount))
+	if (atomic_inc_and_test(&page->_mapcount)) {
 		inc_page_state(nr_mapped);
+		return 1;
+	}
+	return 0;
 }
 
 /**
@@ -479,8 +484,10 @@ void page_add_file_rmap(struct page *pag
  * @page: page to remove mapping from
  *
  * The caller needs to hold the pte lock.
+ *
+ * Return 1 if the removal resulted in the page to become unmapped.
  */
-void page_remove_rmap(struct page *page)
+int page_remove_rmap(struct page *page)
 {
 	if (atomic_add_negative(-1, &page->_mapcount)) {
 		BUG_ON(page_mapcount(page) < 0);
@@ -496,7 +503,9 @@ void page_remove_rmap(struct page *page)
 		if (page_test_and_clear_dirty(page))
 			set_page_dirty(page);
 		dec_page_state(nr_mapped);
+		return 1;
 	}
+	return 0;
 }
 
 /*
@@ -559,10 +568,13 @@ static int try_to_unmap_one(struct page 
 		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
 		BUG_ON(pte_file(*pte));
 		dec_mm_counter(mm, anon_rss);
-	} else
+		page_remove_rmap(page);
+	} else {
 		dec_mm_counter(mm, file_rss);
+		if (page_remove_rmap(page))
+			atomic_inc(&page_zone(page)->pages_unmapped);
+	}
 
-	page_remove_rmap(page);
 	page_cache_release(page);
 
 out_unmap: