+/**
+ * vmballoon_shrinker_scan() - deflate the balloon due to memory pressure.
+ * @shrinker: pointer to the balloon shrinker.
+ * @sc: page reclaim information.
+ *
+ * Returns: number of pages that were freed during deflation.
+ */
+static unsigned long vmballoon_shrinker_scan(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ struct vmballoon *b = &balloon;
+ unsigned long deflated_frames;
+
+ pr_debug("%s - size: %llu", __func__, atomic64_read(&b->size));
+
+ vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_SHRINK);
+
+ /*
+ * If the lock is also contended for read, we cannot easily reclaim and
+ * we bail out.
+ */
+ if (!down_read_trylock(&b->conf_sem))
+ return 0;
+
+ deflated_frames = vmballoon_deflate(b, sc->nr_to_scan, true);
+
+ vmballoon_stats_gen_add(b, VMW_BALLOON_STAT_SHRINK_FREE,
+ deflated_frames);
+
+ /*
+ * Delay future inflation for some time to mitigate the situations in
+ * which balloon continuously grows and shrinks. Use WRITE_ONCE() since
+ * the access is asynchronous.
+ */
+ WRITE_ONCE(b->shrink_timeout, jiffies + HZ * VMBALLOON_SHRINK_DELAY);
+
+ up_read(&b->conf_sem);
+
+ return deflated_frames;
+}
+
+/**
+ * vmballoon_shrinker_count() - return the number of ballooned pages.
+ * @shrinker: pointer to the balloon shrinker.
+ * @sc: page reclaim information.
+ *
+ * Returns: number of 4k pages that are allocated for the balloon and can
+ * therefore be reclaimed under pressure.
+ */
+static unsigned long vmballoon_shrinker_count(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ struct vmballoon *b = &balloon;
+
+ return atomic64_read(&b->size);
+}
+
+static void vmballoon_unregister_shrinker(struct vmballoon *b)
+{
+ if (b->shrinker_registered)
+ unregister_shrinker(&b->shrinker);
+ b->shrinker_registered = false;
+}
+
+static int vmballoon_register_shrinker(struct vmballoon *b)
+{
+ int r;
+
+ /* Do nothing if the shrinker is not enabled */
+ if (!vmwballoon_shrinker_enable)
+ return 0;
+
+ b->shrinker.scan_objects = vmballoon_shrinker_scan;
+ b->shrinker.count_objects = vmballoon_shrinker_count;
+ b->shrinker.seeks = DEFAULT_SEEKS;
+
+ r = register_shrinker(&b->shrinker);
+
+ if (r == 0)
+ b->shrinker_registered = true;
+
+ return r;
+}
+