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thp: move khugepaged_mutex out of khugepaged 

Currently, hugepaged_mutex is used really complexly and hard to
understand, actually, it is just used to serialize start_khugepaged and
khugepaged for these reasons:

- khugepaged_thread is shared between them
- the thp disable path (echo never > transparent_hugepage/enabled) is
  nonblocking, so we need to protect khugepaged_thread to get a stable
  running state

These can be avoided by:

- use the lock to serialize the thread creation and cancel
- thp disable path can not finised until the thread exits

Then khugepaged_thread is fully controlled by start_khugepaged, khugepaged
will be happy without the lock

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Xiao Guangrong 2012-10-08 16:29:41 -07:00 committed by Linus Torvalds
parent 637e3a27ec
commit 911891afe1
1 changed files with 13 additions and 23 deletions
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36
mm/huge_memory.c
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@ -139,9 +139,6 @@ static int start_khugepaged(void)
{
int err = 0;
if (khugepaged_enabled()) {
int wakeup;
mutex_lock(&khugepaged_mutex);
if (!khugepaged_thread)
khugepaged_thread = kthread_run(khugepaged, NULL,
"khugepaged");
@ -151,15 +148,17 @@ static int start_khugepaged(void)
err = PTR_ERR(khugepaged_thread);
khugepaged_thread = NULL;
}
wakeup = !list_empty(&khugepaged_scan.mm_head);
mutex_unlock(&khugepaged_mutex);
if (wakeup)
if (!list_empty(&khugepaged_scan.mm_head))
wake_up_interruptible(&khugepaged_wait);
set_recommended_min_free_kbytes();
} else
} else if (khugepaged_thread) {
/* wakeup to exit */
wake_up_interruptible(&khugepaged_wait);
kthread_stop(khugepaged_thread);
khugepaged_thread = NULL;
}
return err;
}
@ -221,7 +220,12 @@ static ssize_t enabled_store(struct kobject *kobj,
TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
if (ret > 0) {
int err = start_khugepaged();
int err;
mutex_lock(&khugepaged_mutex);
err = start_khugepaged();
mutex_unlock(&khugepaged_mutex);
if (err)
ret = err;
}
@ -2329,20 +2333,10 @@ static int khugepaged(void *none)
set_freezable();
set_user_nice(current, 19);
/* serialize with start_khugepaged() */
mutex_lock(&khugepaged_mutex);
for (;;) {
mutex_unlock(&khugepaged_mutex);
while (!kthread_should_stop()) {
VM_BUG_ON(khugepaged_thread != current);
khugepaged_loop();
VM_BUG_ON(khugepaged_thread != current);
mutex_lock(&khugepaged_mutex);
if (!khugepaged_enabled())
break;
if (unlikely(kthread_should_stop()))
break;
}
spin_lock(&khugepaged_mm_lock);
@ -2351,10 +2345,6 @@ static int khugepaged(void *none)
if (mm_slot)
collect_mm_slot(mm_slot);
spin_unlock(&khugepaged_mm_lock);
khugepaged_thread = NULL;
mutex_unlock(&khugepaged_mutex);
return 0;
}