On Mon 18-10-21 13:05:35, Vasily Averin wrote: > On 18.10.2021 12:04, Michal Hocko wrote: > > On Mon 18-10-21 11:13:52, Vasily Averin wrote: > > [...] > >> How could this happen? > >> > >> User-space task inside the memcg-limited container generated a page fault, > >> its handler do_user_addr_fault() called handle_mm_fault which could not > >> allocate the page due to exceeding the memcg limit and returned VM_FAULT_OOM. > >> Then do_user_addr_fault() called pagefault_out_of_memory() which executed > >> out_of_memory() without set of memcg. > >> > >> Partially this problem depends on one of my recent patches, disabled unlimited > >> memory allocation for dying tasks. However I think the problem can happen > >> on non-killed tasks too, for example because of kmem limit. > > > > Could you be more specific on how this can happen without your patch? I > > have to say I haven't realized this side effect when discussing it. > > We can reach obj_cgroup_charge_pages() for example via > > do_user_addr_fault > handle_mm_fault > __handle_mm_fault > p4d_alloc > __p4d_alloc > p4d_alloc_one > get_zeroed_page > __get_free_pages > alloc_pages > __alloc_pages > __memcg_kmem_charge_page > obj_cgroup_charge_pages > > Here we call try_charge_memcg() that return success and approve the allocation, > however then we hit into kmem limit and fail the allocation. Just to make sure I understand this would be for the v1 kmem explicit limit, correct? > If required I can try to search how try_charge_memcg() can reject page allocation > of non-dying task too. Yes. > > I will be honest that I am not really happy about pagefault_out_of_memory. > > I have tried to remove it in the past. Without much success back then, > > unfortunately[1]. > > Maybe we should get rid of it finally. The OOM is always triggered from > > inside the allocator where we have much more infromation about the > > allocation context. A first step would be to skip pagefault_out_of_memory > > for killed or exiting processes. > > I like this idea, however it may be not enough, at least in scenario described above. I original patch has removed the oom killer completely. -- Michal Hocko SUSE Labs
