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>
diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt
index 00c3d31..8458c08 100644
--- a/Documentation/vm/zswap.txt
+++ b/Documentation/vm/zswap.txt
@@ -26,8 +26,22 @@
device when the compressed pool reaches its size limit. This requirement had
been identified in prior community discussions.
-To enabled zswap, the "enabled" attribute must be set to 1 at boot time. e.g.
-zswap.enabled=1
+Zswap is disabled by default but can be enabled at boot time by setting
+the "enabled" attribute to 1 at boot time. ie: zswap.enabled=1. Zswap
+can also be enabled and disabled at runtime using the sysfs interface.
+An example command to enable zswap at runtime, assuming sysfs is mounted
+at /sys, is:
+
+echo 1 > /sys/modules/zswap/parameters/enabled
+
+When zswap is disabled at runtime it will stop storing pages that are
+being swapped out. However, it will _not_ immediately write out or fault
+back into memory all of the pages stored in the compressed pool. The
+pages stored in zswap will remain in the compressed pool until they are
+either invalidated or faulted back into memory. In order to force all
+pages out of the compressed pool, a swapoff on the swap device(s) will
+fault back into memory all swapped out pages, including those in the
+compressed pool.
Design:
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 @@
/*********************************
* 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 @@
u8 *src, *dst;
struct zswap_header *zhdr;
- if (!tree) {
+ if (!zswap_enabled || !tree) {
ret = -ENODEV;
goto reject;
}
@@ -901,9 +902,6 @@
{
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,
