From: Hugh Dickins hughd@google.com
commit 8d22a9351035ef2ff12ef163a1091b8b8cf1e49c upstream.
It was hard to keep a test running, moving tasks between memcgs with move_charge_at_immigrate, while swapping: mem_cgroup_id_get_many()'s refcount is discovered to be 0 (supposedly impossible), so it is then forced to REFCOUNT_SATURATED, and after thousands of warnings in quick succession, the test is at last put out of misery by being OOM killed.
This is because of the way moved_swap accounting was saved up until the task move gets completed in __mem_cgroup_clear_mc(), deferred from when mem_cgroup_move_swap_account() actually exchanged old and new ids. Concurrent activity can free up swap quicker than the task is scanned, bringing id refcount down 0 (which should only be possible when offlining).
Just skip that optimization: do that part of the accounting immediately.
Fixes: 615d66c37c75 ("mm: memcontrol: fix memcg id ref counter on swap charge move") Signed-off-by: Hugh Dickins hughd@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Alex Shi alex.shi@linux.alibaba.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Alex Shi alex.shi@linux.alibaba.com Cc: Shakeel Butt shakeelb@google.com Cc: Michal Hocko mhocko@suse.com Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2007071431050.4726@eggly.anvils Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4794,7 +4794,6 @@ static void __mem_cgroup_clear_mc(void) if (!mem_cgroup_is_root(mc.to)) page_counter_uncharge(&mc.to->memory, mc.moved_swap);
- mem_cgroup_id_get_many(mc.to, mc.moved_swap); css_put_many(&mc.to->css, mc.moved_swap);
mc.moved_swap = 0; @@ -4972,7 +4971,8 @@ put: /* get_mctgt_type() gets the page ent = target.ent; if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to)) { mc.precharge--; - /* we fixup refcnts and charges later. */ + mem_cgroup_id_get_many(mc.to, 1); + /* we fixup other refcnts and charges later. */ mc.moved_swap++; } break;