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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>
This commit is contained in:
Hugh Dickins 2009-09-21 17:02:14 -07:00 committed by Linus Torvalds
parent 26465d3ea5
commit 6e15838425
1 changed files with 22 additions and 6 deletions
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28
mm/ksm.c
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@ -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;
}