Messages in this thread Patch in this message | | | Date | Mon, 3 Aug 2009 13:14:03 +0100 (BST) | From | Hugh Dickins <> | Subject | [PATCH 5/12] ksm: keep quiet while list empty |
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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> ---
mm/ksm.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-)
--- ksm4/mm/ksm.c 2009-08-02 13:49:59.000000000 +0100 +++ ksm5/mm/ksm.c 2009-08-02 13:50:07.000000000 +0100 @@ -1287,21 +1287,27 @@ static void ksm_do_scan(unsigned int sca } } +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; @@ -1346,10 +1352,16 @@ int ksm_madvise(struct vm_area_struct *v 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); /* @@ -1361,6 +1373,10 @@ 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; }
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