[PATCH] zswap: Add shrink_enabled that can disable swap shrink to increase store performance

[Hui Zhu <teawaterz@linux.alibaba.com>]

zswap will try to shrink pool when zswap is full.
This commit add shrink_enabled that can disable swap shrink to increase
store performance.  User can disable swap shrink if care about the store
performance.

For example in a VM with 1 CPU 1G memory 4G swap:
echo lz4 > /sys/module/zswap/parameters/compressor
echo z3fold > /sys/module/zswap/parameters/zpool
echo 0 > /sys/module/zswap/parameters/same_filled_pages_enabled
echo 1 > /sys/module/zswap/parameters/enabled
usemem -a -n 1 $((4000 * 1024 * 1024))
4718592000 bytes / 114937822 usecs = 40091 KB/s
101700 usecs to free memory
echo 0 > /sys/module/zswap/parameters/shrink_enabled
usemem -a -n 1 $((4000 * 1024 * 1024))
4718592000 bytes / 8837320 usecs = 521425 KB/s
129577 usecs to free memory

The store speed increased when zswap shrink disabled.

Signed-off-by: Hui Zhu <teawaterz@linux.alibaba.com>
---
 mm/zswap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/zswap.c b/mm/zswap.c
index 46a3223..731e3d1e 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -114,6 +114,10 @@ static bool zswap_same_filled_pages_enabled = true;
 module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled,
 		   bool, 0644);
 
+/* Enable/disable zswap shrink (enabled by default) */
+static bool zswap_shrink_enabled = true;
+module_param_named(shrink_enabled, zswap_shrink_enabled, bool, 0644);
+
 /*********************************
 * data structures
 **********************************/
@@ -947,6 +951,9 @@ static int zswap_shrink(void)
 	struct zswap_pool *pool;
 	int ret;
 
+	if (!zswap_shrink_enabled)
+		return -EPERM;
+
 	pool = zswap_pool_last_get();
 	if (!pool)
 		return -ENOENT;
-- 
2.7.4