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 <>
Acked-by: default avatarIzik Eidus <>
Cc: Andrea Arcangeli <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 26465d3e
......@@ -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) {
if (ksmd_should_run())
if (ksmd_should_run()) {
} else {
(ksm_run & KSM_RUN_MERGE) ||
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);
insert_to_mm_slots_hash(mm, mm_slot);
......@@ -1354,6 +1366,10 @@ int __ksm_enter(struct mm_struct *mm)
set_bit(MMF_VM_MERGEABLE, &mm->flags);
if (needs_wakeup)
return 0;
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