On Mon 13-09-21 12:37:56, Vasily Averin wrote: > On 9/13/21 11:39 AM, Michal Hocko wrote: > > On Mon 13-09-21 10:51:37, Vasily Averin wrote: > >> On 9/10/21 3:39 PM, Vasily Averin wrote: > >>> The kernel currently allows dying tasks to exceed the memcg limits. > >>> The allocation is expected to be the last one and the occupied memory > >>> will be freed soon. > >>> This is not always true because it can be part of the huge vmalloc > >>> allocation. Allowed once, they will repeat over and over again. > >> > >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c > >>> index 389b5766e74f..67195fcfbddf 100644 > >>> --- a/mm/memcontrol.c > >>> +++ b/mm/memcontrol.c > >>> @@ -2622,15 +2625,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, > >>> if (gfp_mask & __GFP_ATOMIC) > >>> goto force; > >>> > >>> - /* > >>> - * Unlike in global OOM situations, memcg is not in a physical > >>> - * memory shortage. Allow dying and OOM-killed tasks to > >>> - * bypass the last charges so that they can exit quickly and > >>> - * free their memory. > >>> - */ > >>> - if (unlikely(should_force_charge())) > >>> - goto force; > >>> - > >> > >> Should we keep current behaviour for (current->flags & PF_EXITING) case perhaps? > > > > Why? > > On this stage task really dies and mostly releases taken resources. > It can allocate though, and this allocation can reach memcg limit due to the activity > of parallel memcg threads. > > Noting bad should happen if we reject this allocation, > because the same thing can happen in non-memcg case too. > However I doubt misuse is possible here and we have possibility to allow graceful shutdown here. > > In other words: we are not obliged to allow such allocations, but we CAN do it because > we hope that it is safe and cannot be misused. This is a lot of hoping that has turned out to be a bad strategy in the existing code. So let's stop hoping and if we are shown that an exit path really benefits from a special treatment then we can add it with a good reasoning rathat than "we hope it's gonna be ok". -- Michal Hocko SUSE Labs
