[PATCH] add /proc/meminfo:Mapped

The patch adds a "Mapped" field to /proc/meminfo - tha amount of memory
which is mapped into pagetables.

This is a useful statistic to monitor when testing and observing the
vitual memory system.

fs/proc/proc_misc.c

@@ -178,6 +178,7 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
 		"SwapFree:     %8lu kB\n"
 		"Dirty:        %8lu kB\n"
 		"Writeback:    %8lu kB\n"
+		"Mapped:       %8lu kB\n"
 		"Committed_AS: %8u kB\n"
 		"PageTables:   %8lu kB\n"
 		"ReverseMaps:  %8lu\n"
@@ -199,6 +200,7 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
 		K(i.freeswap),
 		K(ps.nr_dirty),
 		K(ps.nr_writeback),
+		K(ps.nr_mapped),
 		K(committed),
 		K(ps.nr_page_table_pages),
 		ps.nr_reverse_maps,

include/linux/page-flags.h

@@ -78,6 +78,7 @@ extern struct page_state {
 	unsigned long nr_pagecache;
 	unsigned long nr_page_table_pages;
 	unsigned long nr_reverse_maps;
+	unsigned long nr_mapped;
 } ____cacheline_aligned_in_smp page_states[NR_CPUS];
 
 extern void get_page_state(struct page_state *ret);

mm/page_alloc.c

@@ -562,6 +562,7 @@ void get_page_state(struct page_state *ret)
 		ret->nr_pagecache += ps->nr_pagecache;
 		ret->nr_page_table_pages += ps->nr_page_table_pages;
 		ret->nr_reverse_maps += ps->nr_reverse_maps;
+		ret->nr_mapped += ps->nr_mapped;
 	}
 }
 

mm/rmap.c

@@ -214,6 +214,7 @@ void page_add_rmap(struct page * page, pte_t * ptep)
 	if (page->pte.direct == 0) {
 		page->pte.direct = pte_paddr;
 		SetPageDirect(page);
+		inc_page_state(nr_mapped);
 		goto out;
 	}
 
@@ -336,6 +337,8 @@ void page_remove_rmap(struct page * page, pte_t * ptep)
 
 out:
 	pte_chain_unlock(page);
+	if (!page_mapped(page))
+		dec_page_state(nr_mapped);
 	return;
 }
 
@@ -501,6 +504,8 @@ int try_to_unmap(struct page * page)
 		}
 	}
 out:
+	if (!page_mapped(page))
+		dec_page_state(nr_mapped);
 	return ret;
 }