diff options
authorSeongJae Park <sjpark@amazon.de>2020-01-27 09:18:08 +0100
committerBoris Ostrovsky <boris.ostrovsky@oracle.com>2020-01-29 07:35:49 -0600
commit8a105678fb3ec4763352db84745968bf2cb4aa65 (patch)
parentxen/gntdev: Do not use mm notifiers with autotranslating guests (diff)
xenbus/backend: Add memory pressure handler callback
Granting pages consumes backend system memory. In systems configured with insufficient spare memory for those pages, it can cause a memory pressure situation. However, finding the optimal amount of the spare memory is challenging for large systems having dynamic resource utilization patterns. Also, such a static configuration might lack flexibility. To mitigate such problems, this commit adds a memory reclaim callback to 'xenbus_driver'. If a memory pressure is detected, 'xenbus' requests every backend driver to volunarily release its memory. Note that it would be able to improve the callback facility for more sophisticated handlings of general pressures. For example, it would be possible to monitor the memory consumption of each device and issue the release requests to only devices which causing the pressure. Also, the callback could be extended to handle not only memory, but general resources. Nevertheless, this version of the implementation defers such sophisticated goals as a future work. Reviewed-by: Juergen Gross <jgross@suse.com> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> Signed-off-by: SeongJae Park <sjpark@amazon.de> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
2 files changed, 33 insertions, 0 deletions
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index 14876faff3b0..3b5cb7a5a7e4 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -247,6 +247,35 @@ static int backend_probe_and_watch(struct notifier_block *notifier,
+static int backend_reclaim_memory(struct device *dev, void *data)
+ const struct xenbus_driver *drv;
+ if (!dev->driver)
+ return 0;
+ drv = to_xenbus_driver(dev->driver);
+ if (drv && drv->reclaim_memory)
+ drv->reclaim_memory(to_xenbus_device(dev));
+ return 0;
+ * Returns 0 always because we are using shrinker to only detect memory
+ * pressure.
+ */
+static unsigned long backend_shrink_memory_count(struct shrinker *shrinker,
+ struct shrink_control *sc)
+ bus_for_each_dev(&xenbus_backend.bus, NULL, NULL,
+ backend_reclaim_memory);
+ return 0;
+static struct shrinker backend_memory_shrinker = {
+ .count_objects = backend_shrink_memory_count,
+ .seeks = DEFAULT_SEEKS,
static int __init xenbus_probe_backend_init(void)
static struct notifier_block xenstore_notifier = {
@@ -263,6 +292,9 @@ static int __init xenbus_probe_backend_init(void)
+ if (register_shrinker(&backend_memory_shrinker))
+ pr_warn("shrinker registration failed\n");
return 0;
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 24228a102141..980952ea452b 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -105,6 +105,7 @@ struct xenbus_driver {
struct device_driver driver;
int (*read_otherend_details)(struct xenbus_device *dev);
int (*is_ready)(struct xenbus_device *dev);
+ void (*reclaim_memory)(struct xenbus_device *dev);
static inline struct xenbus_driver *to_xenbus_driver(struct device_driver *drv)