On Wed 26-08-20 21:47:02, Xunlei Pang wrote: > We've met softlockup with "CONFIG_PREEMPT_NONE=y", when > the target memcg doesn't have any reclaimable memory. > > It can be easily reproduced as below: > watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204] > CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12 > Call Trace: > shrink_lruvec+0x49f/0x640 > shrink_node+0x2a6/0x6f0 > do_try_to_free_pages+0xe9/0x3e0 > try_to_free_mem_cgroup_pages+0xef/0x1f0 > try_charge+0x2c1/0x750 > mem_cgroup_charge+0xd7/0x240 > __add_to_page_cache_locked+0x2fd/0x370 > add_to_page_cache_lru+0x4a/0xc0 > pagecache_get_page+0x10b/0x2f0 > filemap_fault+0x661/0xad0 > ext4_filemap_fault+0x2c/0x40 > __do_fault+0x4d/0xf9 > handle_mm_fault+0x1080/0x1790 > > It only happens on our 1-vcpu instances, because there's no chance > for oom reaper to run to reclaim the to-be-killed process. > > Add cond_resched() at the upper shrink_node_memcgs() to solve this > issue, and any other possible issue like meomry.min protection.
I would just add " This will mean that we will get a scheduling point for each memcg in the reclaimed hierarchy without any dependency on the reclaimable memory in that memcg thus making it more predictable. " > Suggested-by: Michal Hocko <[email protected]> > Signed-off-by: Xunlei Pang <[email protected]> Acked-by: Michal Hocko <[email protected]> Thanks! > --- > mm/vmscan.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 99e1796..bbdc38b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2617,6 +2617,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct > scan_control *sc) > > mem_cgroup_calculate_protection(target_memcg, memcg); > > + cond_resched(); > + > if (mem_cgroup_below_min(memcg)) { > /* > * Hard protection. > -- > 1.8.3.1 -- Michal Hocko SUSE Labs
