ksm: Provide support to use deferred timers for scanner thread
KSM thread to scan pages is getting schedule on definite timeout.
That wakes up CPU from idle state and hence may affect the power
consumption. Provide an optional support to use deferred timer
which suites low-power use-cases.
To enable deferred timers,
$ echo 1 > /sys/kernel/mm/ksm/deferred_timer
Change-Id: I07fe199f97fe1f72f9a9e1b0b757a3ac533719e8
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
diff --git a/Documentation/vm/ksm.txt b/Documentation/vm/ksm.txt
index f34a8ee6..f40b965 100644
--- a/Documentation/vm/ksm.txt
+++ b/Documentation/vm/ksm.txt
@@ -87,6 +87,13 @@
pages_unshared - how many pages unique but repeatedly checked for merging
pages_volatile - how many pages changing too fast to be placed in a tree
full_scans - how many times all mergeable areas have been scanned
+deferred_timer - whether to use deferred timers or not
+ e.g. "echo 1 > /sys/kernel/mm/ksm/deferred_timer"
+ Default: 0 (means, we are not using deferred timers. Users
+ might want to set deferred_timer option if they donot want
+ ksm thread to wakeup CPU to carryout ksm activities thus
+ gaining on battery while compromising slightly on memory
+ that could have been saved.)
A high ratio of pages_sharing to pages_shared indicates good sharing, but
a high ratio of pages_unshared to pages_sharing indicates wasted effort.
diff --git a/mm/ksm.c b/mm/ksm.c
index 9ae6011..f270acc 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -223,6 +223,9 @@
/* Milliseconds ksmd should sleep between batches */
static unsigned int ksm_thread_sleep_millisecs = 20;
+/* Boolean to indicate whether to use deferred timer or not */
+static bool use_deferred_timer;
+
#ifdef CONFIG_NUMA
/* Zeroed when merging across nodes is not allowed */
static unsigned int ksm_merge_across_nodes = 1;
@@ -1705,6 +1708,41 @@
}
}
+static void process_timeout(unsigned long __data)
+{
+ wake_up_process((struct task_struct *)__data);
+}
+
+static signed long __sched deferred_schedule_timeout(signed long timeout)
+{
+ struct timer_list timer;
+ unsigned long expire;
+
+ __set_current_state(TASK_INTERRUPTIBLE);
+ if (timeout < 0) {
+ pr_err("schedule_timeout: wrong timeout value %lx\n",
+ timeout);
+ __set_current_state(TASK_RUNNING);
+ goto out;
+ }
+
+ expire = timeout + jiffies;
+
+ setup_deferrable_timer_on_stack(&timer, process_timeout,
+ (unsigned long)current);
+ mod_timer(&timer, expire);
+ schedule();
+ del_singleshot_timer_sync(&timer);
+
+ /* Remove the timer from the object tracker */
+ destroy_timer_on_stack(&timer);
+
+ timeout = expire - jiffies;
+
+out:
+ return timeout < 0 ? 0 : timeout;
+}
+
static int ksmd_should_run(void)
{
return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
@@ -1725,7 +1763,11 @@
try_to_freeze();
if (ksmd_should_run()) {
- schedule_timeout_interruptible(
+ if (use_deferred_timer)
+ deferred_schedule_timeout(
+ msecs_to_jiffies(ksm_thread_sleep_millisecs));
+ else
+ schedule_timeout_interruptible(
msecs_to_jiffies(ksm_thread_sleep_millisecs));
} else {
wait_event_freezable(ksm_thread_wait,
@@ -2175,6 +2217,26 @@
}
KSM_ATTR(run);
+static ssize_t deferred_timer_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return snprintf(buf, 8, "%d\n", use_deferred_timer);
+}
+
+static ssize_t deferred_timer_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned long enable;
+ int err;
+
+ err = kstrtoul(buf, 10, &enable);
+ use_deferred_timer = enable;
+
+ return count;
+}
+KSM_ATTR(deferred_timer);
+
#ifdef CONFIG_NUMA
static ssize_t merge_across_nodes_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
@@ -2287,6 +2349,7 @@
&pages_unshared_attr.attr,
&pages_volatile_attr.attr,
&full_scans_attr.attr,
+ &deferred_timer_attr.attr,
#ifdef CONFIG_NUMA
&merge_across_nodes_attr.attr,
#endif