ksm: keep quiet while list empty
ksm_scan_thread already sleeps in wait_event_interruptible until setting
ksm_run activates it; but if there's nothing on its list to look at, i.e.
nobody has yet said madvise MADV_MERGEABLE, it's a shame to be clocking
up system time and full_scans: ksmd_should_run added to check that too.
And move the mutex_lock out around it: the new counts showed that when
ksm_run is stopped, a little work often got done afterwards, because it
had been read before taking the mutex.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/ksm.c b/mm/ksm.c
index 81f692e..2849422 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1280,21 +1280,27 @@
}
}
+static int ksmd_should_run(void)
+{
+ return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
+}
+
static int ksm_scan_thread(void *nothing)
{
set_user_nice(current, 5);
while (!kthread_should_stop()) {
- if (ksm_run & KSM_RUN_MERGE) {
- mutex_lock(&ksm_thread_mutex);
+ mutex_lock(&ksm_thread_mutex);
+ if (ksmd_should_run())
ksm_do_scan(ksm_thread_pages_to_scan);
- mutex_unlock(&ksm_thread_mutex);
+ mutex_unlock(&ksm_thread_mutex);
+
+ if (ksmd_should_run()) {
schedule_timeout_interruptible(
msecs_to_jiffies(ksm_thread_sleep_millisecs));
} else {
wait_event_interruptible(ksm_thread_wait,
- (ksm_run & KSM_RUN_MERGE) ||
- kthread_should_stop());
+ ksmd_should_run() || kthread_should_stop());
}
}
return 0;
@@ -1339,10 +1345,16 @@
int __ksm_enter(struct mm_struct *mm)
{
- struct mm_slot *mm_slot = alloc_mm_slot();
+ struct mm_slot *mm_slot;
+ int needs_wakeup;
+
+ mm_slot = alloc_mm_slot();
if (!mm_slot)
return -ENOMEM;
+ /* Check ksm_run too? Would need tighter locking */
+ needs_wakeup = list_empty(&ksm_mm_head.mm_list);
+
spin_lock(&ksm_mmlist_lock);
insert_to_mm_slots_hash(mm, mm_slot);
/*
@@ -1354,6 +1366,10 @@
spin_unlock(&ksm_mmlist_lock);
set_bit(MMF_VM_MERGEABLE, &mm->flags);
+
+ if (needs_wakeup)
+ wake_up_interruptible(&ksm_thread_wait);
+
return 0;
}