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-rw-r--r--mm/vmscan.c24
1 files changed, 13 insertions, 11 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bd9a72bc4a1b..ab2505c3ef54 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2921,18 +2921,20 @@ 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);
}