On Wed 17-02-16 19:29:33, Tetsuo Handa wrote: > >From 142b08258e4c60834602e9b0a734564208bc6397 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Date: Wed, 17 Feb 2016 16:29:29 +0900 > Subject: [PATCH 1/6] mm,oom: exclude TIF_MEMDIE processes from candidates. > > The OOM reaper kernel thread can reclaim OOM victim's memory before > the victim releases it. If this is aimed to be preparatory work, which I am not convinced about to be honest, then referring to oom reaper is confusing and misleading. > But it is possible that a TIF_MEMDIE thread > gets stuck at down_read(&mm->mmap_sem) in exit_mm() called from > do_exit() due to one of !TIF_MEMDIE threads doing a GFP_KERNEL > allocation between down_write(&mm->mmap_sem) and up_write(&mm->mmap_sem) > (e.g. mmap()). In that case, we need to use SysRq-f (manual invocation > of the OOM killer) because down_read_trylock(&mm->mmap_sem) by the OOM > reaper will not succeed. But all the tasks sharing the mm with the oom victim will have fatal_signal_pending and so they will get access to memory reserves and that should help them to finish the allocation request. So the above text is misleading. If the down_read is blocked because down_write is blocked then a better solution is to make down_write_killable which has been already proposed. > Also, there are other situations where the OOM > reaper cannot reap the victim's memory (e.g. CONFIG_MMU=n, there was no clear evidence that this is a problem on !MMU configurations. > victim's memory is shared with OOM-unkillable processes) which will > require manual SysRq-f for making progress. Sharing mm with a task which is hidden from the OOM killer is a clear misconfiguration IMO. > However, it is possible that the OOM killer chooses the same OOM victim > forever which already has TIF_MEMDIE. This can happen only for the sysrq+f case AFAICS. Regular OOM killer will stop scanning after it encounters the first TIF_MEMDIE task. If you want to handle the sysrq+f case then it should be imho explicit. Something I've tries here as patch 1/2 http://lkml.kernel.org/r/1452632425-20191-1-git-send-email-mhocko@xxxxxxxxxx which has been nacked. Maybe you can try again without fatal_signal_pending resp. task_will_free_mem checks which were controversial back then. Hiding this into find_lock_non_victim_task_mm is just making the code more obscure and harder to read. > This is effectively disabling > SysRq-f. This patch excludes processes which has a TIF_MEMDIE thread > from OOM victim candidates. > > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> In short I dislike this patch. It makes the code harder to read and the same can be solved more straightforward: diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 078e07ec0906..68cc130c163b 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -281,6 +281,8 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc, if (test_tsk_thread_flag(task, TIF_MEMDIE)) { if (!is_sysrq_oom(oc)) return OOM_SCAN_ABORT; + else + return OOM_SCAN_CONTINUE; } if (!task->mm) return OOM_SCAN_CONTINUE; @@ -719,6 +721,9 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, if (process_shares_mm(child, p->mm)) continue; + + if (is_sysrq_oom(oc) && test_tsk_thread_flag(child, TIF_MEMDIE)) + continue; /* * oom_badness() returns 0 if the thread is unkillable */ -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>