[PATCH] Wait regardless of congestion if too many pages are isolated

[Minchan Kim]

Suddenly, many processes could enter into the direct reclaim path
regradless of congestion. backing dev congestion is just one of them.
But current implementation calls congestion_wait if too many pages are isolated.

if congestion_wait returns without calling io_schedule_timeout,
too_many_isolated can schedule_timeout to wait for the system's calm
to preventing OOM killing.

Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
---
 mm/backing-dev.c |    5 ++---
 mm/compaction.c  |    6 +++++-
 mm/vmscan.c      |    6 +++++-
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 6abe860..9431bca 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -756,8 +756,7 @@ EXPORT_SYMBOL(set_bdi_congested);
  * @timeout: timeout in jiffies
  *
  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
- * write congestion.  If no backing_devs are congested then just wait for the
- * next write to be completed.
+ * write congestion.  If no backing_devs are congested then just returns.
  */  
 long congestion_wait(int sync, long timeout)
 {
@@ -776,7 +775,7 @@ long congestion_wait(int sync, long timeout)
        if (atomic_read(&nr_bdi_congested[sync]) == 0) {
                unnecessary = true;
                cond_resched();
-               ret = 0;
+               ret = timeout;
        } else {
                prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
                ret = io_schedule_timeout(timeout);
diff --git a/mm/compaction.c b/mm/compaction.c
index 94cce51..7370683 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -253,7 +253,11 @@ static unsigned long isolate_migratepages(struct zone *zone,
         * delay for some time until fewer pages are isolated
         */  
        while (unlikely(too_many_isolated(zone))) {
-               congestion_wait(BLK_RW_ASYNC, HZ/10);
+               long timeout = HZ/10;
+               if (timeout == congestion_wait(BLK_RW_ASYNC, timeout)) {
+                       set_current_state(TASK_INTERRUPTIBLE);
+                       schedule_timeout(timeout);
+               }

                if (fatal_signal_pending(current))
                        return 0;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3109ff7..f5e3e28 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1337,7 +1337,11 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
        unsigned long nr_dirty;
        while (unlikely(too_many_isolated(zone, file, sc))) {
-               congestion_wait(BLK_RW_ASYNC, HZ/10);
+               long timeout = HZ/10;
+               if (timeout == congestion_wait(BLK_RW_ASYNC, timeout)) {
+                       set_current_state(TASK_INTERRUPTIBLE);
+                       schedule_timeout(timeout);
+               }

                /* We are about to die and free our memory. Return now. */
                if (fatal_signal_pending(current))
-- 
1.7.0.5


-- 
Kind regards,
Minchan Kim
--
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