Subject: freeze khugepaged and ksmd

From: Andrea Arcangeli <aarcange@redhat.com>

It's unclear why schedule friendly kernel threads can't be taken away by the
CPU through the scheduler itself. It's safer to stop them as they can trigger
memory allocation, if kswapd also freezes itself to avoid generating I/O they
have too.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -15,6 +15,7 @@
 #include <linux/mm_inline.h>
 #include <linux/kthread.h>
 #include <linux/khugepaged.h>
+#include <linux/freezer.h>
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
 #include "internal.h"
@@ -2053,6 +2054,9 @@ static void khugepaged_do_scan(struct pa
 			break;
 #endif
 
+		if (unlikely(kthread_should_stop() || freezing(current)))
+			break;
+
 		spin_lock(&khugepaged_mm_lock);
 		if (!khugepaged_scan.mm_slot)
 			pass_through_head++;
@@ -2115,6 +2119,9 @@ static void khugepaged_loop(void)
 		if (hpage)
 			put_page(hpage);
 #endif
+		try_to_freeze();
+		if (unlikely(kthread_should_stop()))
+			break;
 		if (khugepaged_has_work()) {
 			DEFINE_WAIT(wait);
 			if (!khugepaged_scan_sleep_millisecs)
@@ -2125,8 +2132,8 @@ static void khugepaged_loop(void)
 					khugepaged_scan_sleep_millisecs));
 			remove_wait_queue(&khugepaged_wait, &wait);
 		} else if (khugepaged_enabled())
-			wait_event_interruptible(khugepaged_wait,
-						 khugepaged_wait_event());
+			wait_event_freezable(khugepaged_wait,
+					     khugepaged_wait_event());
 	}
 }
 
@@ -2134,6 +2141,7 @@ static int khugepaged(void *none)
 {
 	struct mm_slot *mm_slot;
 
+	set_freezable();
 	set_user_nice(current, 19);
 
 	/* serialize with start_khugepaged() */
@@ -2148,6 +2156,8 @@ static int khugepaged(void *none)
 		mutex_lock(&khugepaged_mutex);
 		if (!khugepaged_enabled())
 			break;
+		if (unlikely(kthread_should_stop()))
+			break;
 	}
 
 	spin_lock(&khugepaged_mm_lock);
diff --git a/mm/ksm.c b/mm/ksm.c
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -34,6 +34,7 @@
 #include <linux/swap.h>
 #include <linux/ksm.h>
 #include <linux/hash.h>
+#include <linux/freezer.h>
 
 #include <asm/tlbflush.h>
 #include "internal.h"
@@ -1372,7 +1373,7 @@ static void ksm_do_scan(unsigned int sca
 	struct rmap_item *rmap_item;
 	struct page *uninitialized_var(page);
 
-	while (scan_npages--) {
+	while (scan_npages-- && likely(!freezing(current))) {
 		cond_resched();
 		rmap_item = scan_get_next_rmap_item(&page);
 		if (!rmap_item)
@@ -1390,6 +1391,7 @@ static int ksmd_should_run(void)
 
 static int ksm_scan_thread(void *nothing)
 {
+	set_freezable();
 	set_user_nice(current, 5);
 
 	while (!kthread_should_stop()) {
@@ -1398,11 +1400,13 @@ static int ksm_scan_thread(void *nothing
 			ksm_do_scan(ksm_thread_pages_to_scan);
 		mutex_unlock(&ksm_thread_mutex);
 
+		try_to_freeze();
+
 		if (ksmd_should_run()) {
 			schedule_timeout_interruptible(
 				msecs_to_jiffies(ksm_thread_sleep_millisecs));
 		} else {
-			wait_event_interruptible(ksm_thread_wait,
+			wait_event_freezable(ksm_thread_wait,
 				ksmd_should_run() || kthread_should_stop());
 		}
 	}