Merge tag 'v3.10.67' into update

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / mm / vmscan.c

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5b680ab2c280d1c3823b4262da457ee560e5543f..1dcef0ceed212f236a09cee1f6d729ed79b98c99 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2784,18 +2784,20 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
                return false;
 
        /*
-        * There is a potential race between when kswapd checks its watermarks
-        * and a process gets throttled. There is also a potential race if
-        * processes get throttled, kswapd wakes, a large process exits therby
-        * balancing the zones that causes kswapd to miss a wakeup. If kswapd
-        * is going to sleep, no process should be sleeping on pfmemalloc_wait
-        * so wake them now if necessary. If necessary, processes will wake
-        * kswapd and get throttled again
+        * The throttled processes are normally woken up in balance_pgdat() as
+        * soon as pfmemalloc_watermark_ok() is true. But there is a potential
+        * race between when kswapd checks the watermarks and a process gets
+        * throttled. There is also a potential race if processes get
+        * throttled, kswapd wakes, a large process exits thereby balancing the
+        * zones, which causes kswapd to exit balance_pgdat() before reaching
+        * the wake up checks. If kswapd is going to sleep, no process should
+        * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
+        * the wake up is premature, processes will wake kswapd and get
+        * throttled again. The difference from wake ups in balance_pgdat() is
+        * that here we are under prepare_to_wait().
         */
-       if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
-               wake_up(&pgdat->pfmemalloc_wait);
-               return false;
-       }
+       if (waitqueue_active(&pgdat->pfmemalloc_wait))
+               wake_up_all(&pgdat->pfmemalloc_wait);
 
        return pgdat_balanced(pgdat, order, classzone_idx);
 }