thp: freeze khugepaged and ksmd

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 5e7d5d35ea82..e2b0afd0a031 100644
--- 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"
@@ -1365,7 +1366,7 @@ static void ksm_do_scan(unsigned int scan_npages)
         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)
@@ -1383,6 +1384,7 @@ static int ksmd_should_run(void)
 
 static int ksm_scan_thread(void *nothing)
 {
+        set_freezable();
         set_user_nice(current, 5);
 
         while (!kthread_should_stop()) {
@@ -1391,11 +1393,13 @@ 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());
                 }
         }