[PATCH] zoned vm counters: convert nr_mapped to per zone counter

nr_mapped is important because it allows a determination of how many pages of
a zone are not mapped, which would allow a more efficient means of determining
when we need to reclaim memory in a zone.

We take the nr_mapped field out of the page state structure and define a new
per zone counter named NR_FILE_MAPPED (the anonymous pages will be split off
from NR_MAPPED in the next patch).

We replace the use of nr_mapped in various kernel locations.  This avoids the
looping over all processors in try_to_free_pages(), writeback, reclaim (swap +
zone reclaim).

[[email protected]: bugfix]
Signed-off-by: Christoph Lameter <[email protected]>
Cc: Trond Myklebust <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/vmstat.c

@@ -401,13 +401,13 @@ struct seq_operations fragmentation_op = {
 
 static char *vmstat_text[] = {
 	/* Zoned VM counters */
+	"nr_mapped",
 
 	/* Page state */
 	"nr_dirty",
 	"nr_writeback",
 	"nr_unstable",
 	"nr_page_table_pages",
-	"nr_mapped",
 	"nr_slab",
 
 	"pgpgin",