balance_dirty_pages doesn't do the required dirty throttling on cgroupv1. See
commit 9badce000e2c ("cgroup, writeback: don't enable cgroup writeback on
traditional hierarchies"). Instead, the kernel depends on writeback throttling
in shrink_folio_list to achieve the same goal. With large memory systems, the
flusher may not be able to writeback quickly enough such that we will start
finding pages in the shrink_folio_list already in writeback. Hence for cgroupv1
let's do a reclaim throttle after waking up the flusher.
The below test which used to fail on a 256GB system completes till the
the file system is full with this change.
root@lp2:/sys/fs/cgroup/memory# mkdir test
root@lp2:/sys/fs/cgroup/memory# cd test/
root@lp2:/sys/fs/cgroup/memory/test# echo 120M > memory.limit_in_bytes
root@lp2:/sys/fs/cgroup/memory/test# echo $$ > tasks
root@lp2:/sys/fs/cgroup/memory/test# dd if=/dev/zero of=/home/kvaneesh/test bs=1M
Killed
Cc: <stable@xxxxxxxxxx>
Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
mm/vmscan.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 04d8b88e5216..388022c5ef2b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2514,8 +2514,20 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
* the flushers simply cannot keep up with the allocation
* rate. Nudge the flusher threads in case they are asleep.
*/
- if (stat.nr_unqueued_dirty == nr_taken)
+ if (stat.nr_unqueued_dirty == nr_taken) {
wakeup_flusher_threads(WB_REASON_VMSCAN);
+ /*
+ * For cgroupv1 dirty throttling is achieved by waking up
+ * the kernel flusher here and later waiting on folios
+ * which are in writeback to finish (see shrink_folio_list()).
+ *
+ * Flusher may not be able to issue writeback quickly
+ * enough for cgroupv1 writeback throttling to work
+ * on a large system.
+ */
+ if (!writeback_throttling_sane(sc))
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
+ }
sc->nr.dirty += stat.nr_dirty;
sc->nr.congested += stat.nr_congested;
--
2.38.1
