xen: tmem: self-ballooning and frontswap-selfshrinking

This patch introduces two in-kernel drivers for Xen transcendent memory
("tmem") functionality that complement cleancache and frontswap.  Both
use control theory to dynamically adjust and optimize memory utilization.
Selfballooning controls the in-kernel Xen balloon driver, targeting a goal
value (vm_committed_as), thus pushing less frequently used clean
page cache pages (through the cleancache code) into Xen tmem where
Xen can balance needs across all VMs residing on the physical machine.
Frontswap-selfshrinking controls the number of pages in frontswap,
driving it towards zero (effectively doing a partial swapoff) when
in-kernel memory pressure subsides, freeing up RAM for other VMs.

More detail is provided in the header comment of xen-selfballooning.c.

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>

[v8: konrad.wilk@oracle.com: set default enablement depending on frontswap]
[v7: konrad.wilk@oracle.com: fix capitalization and punctuation in comments]
[v6: fix frontswap-selfshrinking initialization]
[v6: konrad.wilk@oracle.com: fix init pr_infos; add comments about swap]
[v5: konrad.wilk@oracle.com: add NULL to attr list; move inits up to decls]
[v4: dkiper@net-space.pl: use strict_strtoul plus a few syntactic nits]
[v3: konrad.wilk@oracle.com: fix potential divides-by-zero]
[v3: konrad.wilk@oracle.com: add many more comments, fix nits]
[v2: rebased to linux-3.0-rc1]
[v2: Ian.Campbell@citrix.com: reorganize as new file (xen-selfballoon.c)]
[v2: dkiper@net-space.pl: proper access to vm_committed_as]
[v2: dkiper@net-space.pl: accounting fixes]
Cc: Jan Beulich <JBeulich@novell.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: <xen-devel@lists.xensource.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index a59638b37c1a..fd3266696a4d 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -9,6 +9,23 @@ config XEN_BALLOON
           the system to expand the domain's memory allocation, or alternatively
           return unneeded memory to the system.
 
+config XEN_SELFBALLOONING
+        bool "Dynamically self-balloon kernel memory to target"
+        depends on XEN && XEN_BALLOON && CLEANCACHE && SWAP
+        default n
+        help
+          Self-ballooning dynamically balloons available kernel memory driven
+          by the current usage of anonymous memory ("committed AS") and
+          controlled by various sysfs-settable parameters.  Configuring
+          FRONTSWAP is highly recommended; if it is not configured, self-
+          ballooning is disabled by default but can be enabled with the
+          'selfballooning' kernel boot parameter.  If FRONTSWAP is configured,
+          frontswap-selfshrinking is enabled by default but can be disabled
+          with the 'noselfshrink' kernel boot parameter; and self-ballooning
+          is enabled by default but can be disabled with the 'noselfballooning'
+          kernel boot parameter.  Note that systems without a sufficiently
+          large swap device should not enable self-ballooning.
+
 config XEN_SCRUB_PAGES
         bool "Scrub pages before returning them to system"
         depends on XEN_BALLOON