[PATCH 1/1] zram: better utilization of zram swap space

[Gopi Sai Teja]

If the length of the compressed page is greater than 75% of the PAGE_SIZE,
then the page is stored uncompressed in zram space. Zram space utilization
is improved if the threshold is 80%(5 compressed pages can be stored in
4 pages).

If the compressed length is greater than 3068 and less than 3261, pages
still can be stored in compressed form in zs_malloc class 3264.
Currently these compressed pages belong to 4096 zs malloc class.

Tested on ARM:
Before Patch:

class  size  obj_allocated   obj_used pages_used
  190  3072           3820       3819       2865
  202  3264             65         63         52
  254  4096          11791      11791      11791

 Total               65604      64616      29504

After Patch:

class  size  obj_allocated   obj_used pages_used
  190  3072           4244       4243       3183
  202  3264           1500       1499       1200
  254  4096           6306       6306       6306

 Total               65983      64896      26628

Signed-off-by: Gopi Sai Teja <gopi.st@xxxxxxxxxxx>
---
 drivers/block/zram/zram_drv.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 5ece255..f7d9ddd 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -31,8 +31,12 @@ static const unsigned max_num_devices = 32;
 /*
  * Pages that compress to size greater than this are stored
  * uncompressed in memory.
+ * 16 is zsmalloc class interval and unsigned long is extra memory
+ * used by zsmalloc to store metadata.
  */
-static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;
+
+static const size_t max_zpage_size = round_down((PAGE_SIZE / 5 * 4), 16)
+					- sizeof(unsigned long);
 
 /*
  * NOTE: max_zpage_size must be less than or equal to:
-- 
1.9.1