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Date: Wed, 24 Jul 2019 08:33:14 +0200
From: Michal Hocko <mhocko@...nel.org>
To: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Cc: mm-commits@...r.kernel.org, shakeelb@...gle.com,
rientjes@...gle.com, mhocko@...e.com, guro@...com,
penguin-kernel@...ove.SAKURA.ne.jp
Subject: Re: + mm-oom-avoid-printk-iteration-under-rcu.patch added to -mm tree
[ups, I've cut the Cc list somehow, sorry about that]
On Wed 24-07-19 08:27:27, Michal Hocko wrote:
> 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-kernel@...ove.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-kernel@I-love.SAKURA.ne.jp
> > Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> > Cc: Shakeel Butt <shakeelb@...gle.com>
> > Cc: Michal Hocko <mhocko@...e.com>
> > Cc: Roman Gushchin <guro@...com>
> > Cc: David Rientjes <rientjes@...gle.com>
> > Signed-off-by: Andrew Morton <akpm@...ux-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-kernel@...ove.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
--
Michal Hocko
SUSE Labs
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