From 6e15838425ac855982f10419558649954a0684a3 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 21 Sep 2009 17:02:14 -0700 Subject: [PATCH] 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 Acked-by: Izik Eidus Cc: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/ksm.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) 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 void ksm_do_scan(unsigned int scan_npages) } } +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_madvise(struct vm_area_struct *vma, unsigned long start, 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 @@ int __ksm_enter(struct mm_struct *mm) spin_unlock(&ksm_mmlist_lock); set_bit(MMF_VM_MERGEABLE, &mm->flags); + + if (needs_wakeup) + wake_up_interruptible(&ksm_thread_wait); + return 0; } -- 2.7.4