mm: add NR_ZSMALLOC to vmstat

zram is very popular for some of the embedded world (e.g., TV, mobile
phones).  On those system, zsmalloc's consumed memory size is never
trivial (one of example from real product system, total memory: 800M,
zsmalloc consumed: 150M), so we have used this out of tree patch to
monitor system memory behavior via /proc/vmstat.

With zsmalloc in vmstat, it helps in tracking down system behavior due
to memory usage.

[[email protected]: zsmalloc: follow up zsmalloc vmstat]
  Link: http://lkml.kernel.org/r/20160607091737.GC23435@bbox
[[email protected]: fix build with CONFIG_ZSMALLOC=m]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Cc: Sangseok Lee <[email protected]>
Cc: Chanho Min <[email protected]>
Cc: Chan Gyun Jeong <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: minchank

include/linux/mmzone.h

@@ -140,6 +140,9 @@ enum zone_stat_item {
 	NR_DIRTIED,		/* page dirtyings since bootup */
 	NR_WRITTEN,		/* page writings since bootup */
 	NR_PAGES_SCANNED,	/* pages scanned since last reclaim */
+#if IS_ENABLED(CONFIG_ZSMALLOC)
+	NR_ZSPAGES,		/* allocated in zsmalloc */
+#endif
 #ifdef CONFIG_NUMA
 	NUMA_HIT,		/* allocated in intended node */
 	NUMA_MISS,		/* allocated in non intended node */

mm/vmstat.c

@@ -718,7 +718,9 @@ const char * const vmstat_text[] = {
 	"nr_dirtied",
 	"nr_written",
 	"nr_pages_scanned",
-
+#if IS_ENABLED(CONFIG_ZSMALLOC)
+	"nr_zspages",
+#endif
 #ifdef CONFIG_NUMA
 	"numa_hit",
 	"numa_miss",

mm/zsmalloc.c

@@ -1007,6 +1007,7 @@ static void __free_zspage(struct zs_pool *pool, struct size_class *class,
 		next = get_next_page(page);
 		reset_page(page);
 		unlock_page(page);
+		dec_zone_page_state(page, NR_ZSPAGES);
 		put_page(page);
 		page = next;
 	} while (page != NULL);
@@ -1137,11 +1138,15 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
 
 		page = alloc_page(gfp);
 		if (!page) {
-			while (--i >= 0)
+			while (--i >= 0) {
+				dec_zone_page_state(pages[i], NR_ZSPAGES);
 				__free_page(pages[i]);
+			}
 			cache_free_zspage(pool, zspage);
 			return NULL;
 		}
+
+		inc_zone_page_state(page, NR_ZSPAGES);
 		pages[i] = page;
 	}