mm: export a function to get vm committed memory

It will be useful to be able to access global memory commitment from
device drivers.  On the Hyper-V platform, the host has a policy engine to
balance the available physical memory amongst all competing virtual
machines hosted on a given node.  This policy engine is driven by a number
of metrics including the memory commitment reported by the guests.  The
balloon driver for Linux on Hyper-V will use this function to retrieve
guest memory commitment.  This function is also used in Xen self
ballooning code.

[akpm@linux-foundation.org: coding-style tweak]
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index 45131b41bcdb..79c3cac87afa 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -66,6 +66,21 @@ int heap_stack_gap = 0;
 
 atomic_long_t mmap_pages_allocated;
 
+/*
+ * The global memory commitment made in the system can be a metric
+ * that can be used to drive ballooning decisions when Linux is hosted
+ * as a guest. On Hyper-V, the host implements a policy engine for dynamically
+ * balancing memory across competing virtual machines that are hosted.
+ * Several metrics drive this policy engine including the guest reported
+ * memory commitment.
+ */
+unsigned long vm_memory_committed(void)
+{
+	return percpu_counter_read_positive(&vm_committed_as);
+}
+
+EXPORT_SYMBOL_GPL(vm_memory_committed);
+
 EXPORT_SYMBOL(mem_map);
 EXPORT_SYMBOL(num_physpages);