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@xxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 36 +++++++++++++-----------------------
1 files changed, 13 insertions(+), 23 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 399e8c9..3715c52 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -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;
}
@@ -2344,20 +2348,10 @@ 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);
@@ -2366,10 +2360,6 @@ 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;
}
--
1.7.7.6
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