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Commit 6e158384 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: default avatarIzik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 26465d3e

mm/ksm.c

+22 −6
Original line number Diff line number Diff line
@@ -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);

		if (ksmd_should_run())

			ksm_do_scan(ksm_thread_pages_to_scan);

		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;

}