[PATCH] vm: add per-zone writeout counter

The VM is supposed to minimise the number of pages which get written off the
LRU (for IO scheduling efficiency, and for high reclaim-success rates).  But
we don't actually have a clear way of showing how true this is.

So add `nr_vmscan_write' to /proc/vmstat and /proc/zoneinfo - the number of
pages which have been written by the vm scanner in this zone and globally.

Cc: Christoph Lameter <clameter@engr.sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/vmstat.c

@@ -465,6 +465,7 @@ static char *vmstat_text[] = {
 	"nr_writeback",
 	"nr_unstable",
 	"nr_bounce",
+	"nr_vmscan_write",
 
 #ifdef CONFIG_NUMA
 	"numa_hit",