memcg: fix memory.high target

When the memory.high threshold is exceeded, try_charge() schedules a
task_work to reclaim the excess.  The reclaim target is set to the
number of pages requested by try_charge().

This is wrong, because try_charge() usually charges more pages than
requested (batch > nr_pages) in order to refill per cpu stocks.  As a
result, a process in a cgroup can easily exceed memory.high
significantly when doing a lot of charges w/o returning to userspace
(e.g.  reading a file in big chunks).

Fix this issue by assuring that when exceeding memory.high a process
reclaims as many pages as were actually charged (i.e.  batch).

Signed-off-by: Vladimir Davydov <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c92a65b2b4ab4103454aa1f8bca828384b22e07b..32259e37a66baf54ccf19f104b915d642d6c3828 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2128,7 +2128,7 @@ done_restock:
         */
        do {
                if (page_counter_read(&memcg->memory) > memcg->high) {
-                       current->memcg_nr_pages_over_high += nr_pages;
+                       current->memcg_nr_pages_over_high += batch;
                        set_notify_resume(current);
                        break;
                }