xen/tmem: Don't use self[ballooning|shrinking] if frontswap is off.

There is no point. We would just squeeze the guest to put more and
more pages in the swap disk without any purpose.

The only time it makes sense to use the selfballooning and shrinking
is when frontswap is being utilized.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 3de01edca3eab53b90331bef25b072cf85ab95d2..6e3b18a8afc6a8749d3d91fd559e2bd5c62cadfc 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3014,7 +3014,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
        tmem.frontswap=0|1 [KNL, XEN]
                        Default is on (1). Disable the usage of the frontswap
-                       API to send swap pages to the hypervisor.
+                       API to send swap pages to the hypervisor. If disabled
+                       the selfballooning and selfshrinking are force disabled.
 
        tmem.selfballooning=0|1 [KNL, XEN]
                        Default is on (1). Disable the driving of swap pages

diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index c1df0ff8987850f568b2f8d6d69f1d61095314e4..18e8bd8fa947994e46b5bd8fb9c09eda29918fa8 100644 (file)
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -403,6 +403,14 @@ static int xen_tmem_init(void)
        }
 #endif
 #ifdef CONFIG_XEN_SELFBALLOONING
+       /*
+        * There is no point of driving pages to the swap system if they
+        * aren't going anywhere in tmem universe.
+        */
+       if (!frontswap) {
+               selfshrinking = false;
+               selfballooning = false;
+       }
        xen_selfballoon_init(selfballooning, selfshrinking);
 #endif
        return 0;

diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c
index 5d637e2b1b9f917a0dc35e90c8259cc377c139f6..f70984a892aa5c16a0e24deaee28acb2497dc9f6 100644 (file)
--- a/drivers/xen/xen-selfballoon.c
+++ b/drivers/xen/xen-selfballoon.c
@@ -53,15 +53,12 @@
  * System configuration note: Selfballooning should not be enabled on
  * systems without a sufficiently large swap device configured; for best
  * results, it is recommended that total swap be increased by the size
- * of the guest memory.  Also, while technically not required to be
- * configured, it is highly recommended that frontswap also be configured
- * and enabled when selfballooning is running.  So, selfballooning
- * is disabled by default if frontswap is not configured and can only
- * be enabled with the "tmem.selfballooning=1" kernel boot option; similarly
- * selfballooning is enabled by default if frontswap is configured and
- * can be disabled with the "tmem.selfballooning=0" kernel boot option.  Finally,
- * when frontswap is configured,frontswap-selfshrinking can be disabled
- * with the "tmem.selfshrink=0" kernel boot option.
+ * of the guest memory. Note, that selfballooning should be disabled by default
+ * if frontswap is not configured.  Similarly selfballooning should be enabled
+ * by default if frontswap is configured and can be disabled with the
+ * "tmem.selfballooning=0" kernel boot option.  Finally, when frontswap is
+ * configured, frontswap-selfshrinking can be disabled  with the
+ * "tmem.selfshrink=0" kernel boot option.
  *
  * Selfballooning is disallowed in domain0 and force-disabled.
  *