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SubjectRe: [PATCH 5/12] ksm: keep quiet while list empty
Hugh Dickins wrote:
> 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;
> }
>
>
ACK


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