When we run stress-ng on the UC (Ubuntu Core), the system will be in a state similar to hang. And we found if a testcase could introduce the oom (like stress-ng-bigheap, stress-ng-brk, ...) under the UC, it is highly possible that this testcase will make the system be in a state like hang. We had a discussion for this issue here: https://github.com/ColinIanKing/stress-ng/pull/270 The root cause are Ubuntu Core is constructed on squashfs, and out_of_memory() will not trigger the oom killer for an allocation without __GFP_FS. For squashfs side: memalloc_nofs_save() squashfs_readahead()--->...--->alloc_page() /* alloc without __GFP_FS */ memalloc_nofs_restore() For oom side: out_of_memory() if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS) && !is_memcg_oom(oc)) return true; In the out_of_memory(), this design exists for a long period of time, If removing these 2 lines, the issue could be fixed. But I don't know if it is allowed to do so or not. From my understanding, there will be no problem to remove those 2 lines, since if the allocation without __GFP_FS triggers the oom killer, the killer will select a process to kill, it has no difference with an allocation with __GFP_FS. Since this design exists for a long time, it is risky to change it, here I use a kthread to trigger oom with __GFP_FS when needed, I think it is a safer way to resolve this issue. Please help review it. Thanks. Hui Wang (1): mm/oom_kill: trigger the oom killer if oom occurs without __GFP_FS mm/oom_kill.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) -- 2.34.1
