Andrew, I've had some concerns wrt. this patch - especially the additional complexity - and I have to say I am not convinced that this is really needed. Our past experience in this area suggests that more tricky code leads to different corner cases. So I am really reluctant to add more complexity without any real world reports.
On Tue 23-07-19 16:14:29, Andrew Morton wrote: > From: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> > Subject: mm, oom: avoid printk() iteration under RCU > > Currently dump_tasks() might call printk() for many thousands times under > RCU, which might take many minutes for slow consoles. Therefore, split > dump_tasks() into three stages; take a snapshot of possible OOM victim > candidates under RCU, dump the snapshot from reschedulable context, and > destroy the snapshot. > > In a future patch, the first stage would be moved to select_bad_process() > and the third stage would be moved to after oom_kill_process(), and will > simplify refcount handling. > > Link: > http://lkml.kernel.org/r/1563360901-8277-1-git-send-email-penguin-ker...@i-love.sakura.ne.jp > Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> > Cc: Shakeel Butt <shake...@google.com> > Cc: Michal Hocko <mho...@suse.com> > Cc: Roman Gushchin <g...@fb.com> > Cc: David Rientjes <rient...@google.com> > Signed-off-by: Andrew Morton <a...@linux-foundation.org> > --- > > include/linux/sched.h | 1 > mm/oom_kill.c | 67 +++++++++++++++++++--------------------- > 2 files changed, 34 insertions(+), 34 deletions(-) > > --- a/include/linux/sched.h~mm-oom-avoid-printk-iteration-under-rcu > +++ a/include/linux/sched.h > @@ -1246,6 +1246,7 @@ struct task_struct { > #ifdef CONFIG_MMU > struct task_struct *oom_reaper_list; > #endif > + struct list_head oom_victim_list; > #ifdef CONFIG_VMAP_STACK > struct vm_struct *stack_vm_area; > #endif > --- a/mm/oom_kill.c~mm-oom-avoid-printk-iteration-under-rcu > +++ a/mm/oom_kill.c > @@ -377,36 +377,13 @@ static void select_bad_process(struct oo > } > } > > -static int dump_task(struct task_struct *p, void *arg) > -{ > - struct oom_control *oc = arg; > - struct task_struct *task; > - > - if (oom_unkillable_task(p)) > - return 0; > > - /* p may not have freeable memory in nodemask */ > - if (!is_memcg_oom(oc) && !oom_cpuset_eligible(p, oc)) > - return 0; > - > - task = find_lock_task_mm(p); > - if (!task) { > - /* > - * This is a kthread or all of p's threads have already > - * detached their mm's. There's no need to report > - * them; they can't be oom killed anyway. > - */ > - return 0; > +static int add_candidate_task(struct task_struct *p, void *arg) > +{ > + if (!oom_unkillable_task(p)) { > + get_task_struct(p); > + list_add_tail(&p->oom_victim_list, (struct list_head *) arg); > } > - > - pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n", > - task->pid, from_kuid(&init_user_ns, task_uid(task)), > - task->tgid, task->mm->total_vm, get_mm_rss(task->mm), > - mm_pgtables_bytes(task->mm), > - get_mm_counter(task->mm, MM_SWAPENTS), > - task->signal->oom_score_adj, task->comm); > - task_unlock(task); > - > return 0; > } > > @@ -422,19 +399,41 @@ static int dump_task(struct task_struct > */ > static void dump_tasks(struct oom_control *oc) > { > - pr_info("Tasks state (memory values in pages):\n"); > - pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes > swapents oom_score_adj name\n"); > + static LIST_HEAD(list); > + struct task_struct *p; > + struct task_struct *t; > > if (is_memcg_oom(oc)) > - mem_cgroup_scan_tasks(oc->memcg, dump_task, oc); > + mem_cgroup_scan_tasks(oc->memcg, add_candidate_task, &list); > else { > - struct task_struct *p; > - > rcu_read_lock(); > for_each_process(p) > - dump_task(p, oc); > + add_candidate_task(p, &list); > rcu_read_unlock(); > } > + pr_info("Tasks state (memory values in pages):\n"); > + pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes > swapents oom_score_adj name\n"); > + list_for_each_entry(p, &list, oom_victim_list) { > + cond_resched(); > + /* p may not have freeable memory in nodemask */ > + if (!is_memcg_oom(oc) && !oom_cpuset_eligible(p, oc)) > + continue; > + /* All of p's threads might have already detached their mm's. */ > + t = find_lock_task_mm(p); > + if (!t) > + continue; > + pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n", > + t->pid, from_kuid(&init_user_ns, task_uid(t)), > + t->tgid, t->mm->total_vm, get_mm_rss(t->mm), > + mm_pgtables_bytes(t->mm), > + get_mm_counter(t->mm, MM_SWAPENTS), > + t->signal->oom_score_adj, t->comm); > + task_unlock(t); > + } > + list_for_each_entry_safe(p, t, &list, oom_victim_list) { > + list_del(&p->oom_victim_list); > + put_task_struct(p); > + } > } > > static void dump_oom_summary(struct oom_control *oc, struct task_struct > *victim) > _ > > Patches currently in -mm which might be from > penguin-ker...@i-love.sakura.ne.jp are > > mm-oom-avoid-printk-iteration-under-rcu.patch > info-task-hung-in-generic_file_write_iter.patch > info-task-hung-in-generic_file_write-fix.patch > kexec-bail-out-upon-sigkill-when-allocating-memory.patch -- Michal Hocko SUSE Labs
