[RFC PATCH v1 3/4] zram: add pages_merged counter to mm_stat

[Alexey Romanov]

This counter shows how many identical compressed
pages have been processed by zram so far.

Signed-off-by: Alexey Romanov <avromanov@xxxxxxxxxxxxxx>
---
 Documentation/admin-guide/blockdev/zram.rst | 2 ++
 drivers/block/zram/zram_drv.c               | 8 ++++++--
 drivers/block/zram/zram_drv.h               | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index e4551579cb12..a1dd202efca1 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -209,6 +209,7 @@ compact           	WO	trigger memory compaction
 debug_stat        	RO	this file is used for zram debugging purposes
 backing_dev	  	RW	set up backend storage for zram to write out
 idle		  	WO	mark allocated slot as idle
+merge           	WO	trigger merge identical pages
 ======================  ======  ===============================================
 
 
@@ -267,6 +268,7 @@ line of text and contains the following stats separated by whitespace:
  pages_compacted  the number of pages freed during compaction
  huge_pages	  the number of incompressible pages
  huge_pages_since the number of incompressible pages since zram set up
+ pages_merged	  the number of identical pages merged into single one
  ================ =============================================================
 
 File /sys/block/zram<id>/bd_stat
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 1dae3564cabd..7a267b37e5db 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1260,7 +1260,7 @@ static ssize_t mm_stat_show(struct device *dev,
 	max_used = atomic_long_read(&zram->stats.max_used_pages);
 
 	ret = scnprintf(buf, PAGE_SIZE,
-			"%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu %8llu\n",
+			"%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu %8llu %8llu\n",
 			orig_size << PAGE_SHIFT,
 			(u64)atomic64_read(&zram->stats.compr_data_size),
 			mem_used << PAGE_SHIFT,
@@ -1269,7 +1269,8 @@ static ssize_t mm_stat_show(struct device *dev,
 			(u64)atomic64_read(&zram->stats.same_pages),
 			atomic_long_read(&pool_stats.pages_compacted),
 			(u64)atomic64_read(&zram->stats.huge_pages),
-			(u64)atomic64_read(&zram->stats.huge_pages_since));
+			(u64)atomic64_read(&zram->stats.huge_pages_since),
+			(u64)atomic64_read(&zram->stats.pages_merged));
 	up_read(&zram->init_lock);
 
 	return ret;
@@ -1473,6 +1474,7 @@ static int zram_cmp_obj_and_merge(struct zram *zram, struct hlist_head *htable,
 				rb_node->cnt++;
 			}
 
+			atomic64_inc(&zram->stats.pages_merged);
 			atomic64_sub(obj_size, &zram->stats.compr_data_size);
 			zram_set_flag(zram, index, ZRAM_MERGED);
 			zram_set_flag(zram, node->index, ZRAM_MERGED);
@@ -1657,6 +1659,8 @@ static void zram_free_page(struct zram *zram, size_t index)
 		} else {
 			mutex_unlock(&zram_rbtree_mutex);
 		}
+
+		atomic64_dec(&zram->stats.pages_merged);
 	} else {
 		zs_free(zram->mem_pool, handle);
 	}
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 4a7151c94523..2afdbf76a1aa 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -88,6 +88,7 @@ struct zram_stats {
 	atomic_long_t max_used_pages;	/* no. of maximum pages stored */
 	atomic64_t writestall;		/* no. of write slow paths */
 	atomic64_t miss_free;		/* no. of missed free */
+	atomic64_t pages_merged;	/* no. of pages, which merged into single one */
 #ifdef	CONFIG_ZRAM_WRITEBACK
 	atomic64_t bd_count;		/* no. of pages in backing device */
 	atomic64_t bd_reads;		/* no. of reads from backing device */
-- 
2.25.1