zswap: runtime enable/disable

Change the "enabled" parameter to be configurable at runtime.  Remove the
enabled check from init(), and move it to the frontswap store() function;
when enabled, pages will be stored, and when disabled, pages won't be
stored.

This is almost identical to Seth's patch from 2 years ago:
http://lkml.iu.edu/hypermail/linux/kernel/1307.2/04289.html

[akpm@linux-foundation.org: tweak documentation]
Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Suggested-by: Seth Jennings <sjennings@variantweb.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 7 deletions

diff --git a/mm/zswap.c b/mm/zswap.c
index 4249e82f..2d5727b 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -75,9 +75,10 @@ static u64 zswap_duplicate_entry;
 /*********************************
 * tunables
 **********************************/
-/* Enable/disable zswap (disabled by default, fixed at boot for now) */
-static bool zswap_enabled __read_mostly;
-module_param_named(enabled, zswap_enabled, bool, 0444);
+
+/* Enable/disable zswap (disabled by default) */
+static bool zswap_enabled;
+module_param_named(enabled, zswap_enabled, bool, 0644);
 
 /* Compressor to be used by zswap (fixed at boot for now) */
 #define ZSWAP_COMPRESSOR_DEFAULT "lzo"
@@ -648,7 +649,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 	u8 *src, *dst;
 	struct zswap_header *zhdr;
 
-	if (!tree) {
+	if (!zswap_enabled || !tree) {
 		ret = -ENODEV;
 		goto reject;
 	}
@@ -901,9 +902,6 @@ static int __init init_zswap(void)
 {
 	gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN;
 
-	if (!zswap_enabled)
-		return 0;
-
 	pr_info("loading zswap\n");
 
 	zswap_pool = zpool_create_pool(zswap_zpool_type, "zswap", gfp,