From: Oleg Nesterov <oleg@redhat.com>
To: Sultan Alsawaf <sultan@kerneltoast.com>
Cc: "Christian Brauner" <christian@brauner.io>,
"Daniel Colascione" <dancol@google.com>,
"Suren Baghdasaryan" <surenb@google.com>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Tim Murray" <timmurray@google.com>,
"Michal Hocko" <mhocko@kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Arve Hjønnevåg" <arve@android.com>,
"Todd Kjos" <tkjos@android.com>,
"Martijn Coenen" <maco@android.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Peter Zijlstra" <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
"open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
linux-mm <linux-mm@kvack.org>,
kernel-team <kernel-team@android.com>,
"Andy Lutomirski" <luto@amacapital.net>,
"Serge E. Hallyn" <serge@hallyn.com>,
"Kees Cook" <keescook@chromium.org>,
"Joel Fernandes" <joel@joelfernandes.org>
Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android
Date: Tue, 7 May 2019 17:31:54 +0200 [thread overview]
Message-ID: <20190507153154.GA5750@redhat.com> (raw)
In-Reply-To: <20190507021622.GA27300@sultan-box.localdomain>
I am not going to comment the intent, but to be honest I am skeptical too.
On 05/06, Sultan Alsawaf wrote:
>
> +static unsigned long find_victims(struct victim_info *varr, int *vindex,
> + int vmaxlen, int min_adj, int max_adj)
> +{
> + unsigned long pages_found = 0;
> + int old_vindex = *vindex;
> + struct task_struct *tsk;
> +
> + for_each_process(tsk) {
> + struct task_struct *vtsk;
> + unsigned long tasksize;
> + short oom_score_adj;
> +
> + /* Make sure there's space left in the victim array */
> + if (*vindex == vmaxlen)
> + break;
> +
> + /* Don't kill current, kthreads, init, or duplicates */
> + if (same_thread_group(tsk, current) ||
> + tsk->flags & PF_KTHREAD ||
> + is_global_init(tsk) ||
> + vtsk_is_duplicate(varr, *vindex, tsk))
> + continue;
> +
> + vtsk = find_lock_task_mm(tsk);
Did you test this patch with lockdep enabled?
If I read the patch correctly, lockdep should complain. vtsk_is_duplicate()
ensures that we do not take the same ->alloc_lock twice or more, but lockdep
can't know this.
> +static void scan_and_kill(unsigned long pages_needed)
> +{
> + static DECLARE_WAIT_QUEUE_HEAD(victim_waitq);
> + struct victim_info victims[MAX_VICTIMS];
> + int i, nr_to_kill = 0, nr_victims = 0;
> + unsigned long pages_found = 0;
> + atomic_t victim_count;
> +
> + /*
> + * Hold the tasklist lock so tasks don't disappear while scanning. This
> + * is preferred to holding an RCU read lock so that the list of tasks
> + * is guaranteed to be up to date. Keep preemption disabled until the
> + * SIGKILLs are sent so the victim kill process isn't interrupted.
> + */
> + read_lock(&tasklist_lock);
> + preempt_disable();
read_lock() disables preemption, every task_lock() too, so this looks
unnecessary.
> + for (i = 1; i < ARRAY_SIZE(adj_prio); i++) {
> + pages_found += find_victims(victims, &nr_victims, MAX_VICTIMS,
> + adj_prio[i], adj_prio[i - 1]);
> + if (pages_found >= pages_needed || nr_victims == MAX_VICTIMS)
> + break;
> + }
> +
> + /*
> + * Calculate the number of tasks that need to be killed and quickly
> + * release the references to those that'll live.
> + */
> + for (i = 0, pages_found = 0; i < nr_victims; i++) {
> + struct victim_info *victim = &victims[i];
> + struct task_struct *vtsk = victim->tsk;
> +
> + /* The victims' mm lock is taken in find_victims; release it */
> + if (pages_found >= pages_needed) {
> + task_unlock(vtsk);
> + continue;
> + }
> +
> + /*
> + * Grab a reference to the victim so it doesn't disappear after
> + * the tasklist lock is released.
> + */
> + get_task_struct(vtsk);
The comment doesn't look correct. the victim can't dissapear until task_unlock()
below, it can't pass exit_mm().
> + pages_found += victim->size;
> + nr_to_kill++;
> + }
> + read_unlock(&tasklist_lock);
> +
> + /* Kill the victims */
> + victim_count = (atomic_t)ATOMIC_INIT(nr_to_kill);
> + for (i = 0; i < nr_to_kill; i++) {
> + struct victim_info *victim = &victims[i];
> + struct task_struct *vtsk = victim->tsk;
> +
> + pr_info("Killing %s with adj %d to free %lu kiB\n", vtsk->comm,
> + vtsk->signal->oom_score_adj,
> + victim->size << (PAGE_SHIFT - 10));
> +
> + /* Configure the victim's mm to notify us when it's freed */
> + vtsk->mm->slmk_waitq = &victim_waitq;
> + vtsk->mm->slmk_counter = &victim_count;
> +
> + /* Accelerate the victim's death by forcing the kill signal */
> + do_send_sig_info(SIGKILL, SIG_INFO_TYPE, vtsk, true);
^^^^
this should be PIDTYPE_TGID
> +
> + /* Finally release the victim's mm lock */
> + task_unlock(vtsk);
> + }
> + preempt_enable_no_resched();
See above. And I don't understand how can _no_resched() really help...
> +
> + /* Try to speed up the death process now that we can schedule again */
> + for (i = 0; i < nr_to_kill; i++) {
> + struct task_struct *vtsk = victims[i].tsk;
> +
> + /* Increase the victim's priority to make it die faster */
> + set_user_nice(vtsk, MIN_NICE);
> +
> + /* Allow the victim to run on any CPU */
> + set_cpus_allowed_ptr(vtsk, cpu_all_mask);
> +
> + /* Finally release the victim reference acquired earlier */
> + put_task_struct(vtsk);
> + }
> +
> + /* Wait until all the victims die */
> + wait_event(victim_waitq, !atomic_read(&victim_count));
Can't we avoid the new slmk_waitq/slmk_counter members in mm_struct?
I mean, can't we export victim_waitq and victim_count and, say, set/test
MMF_OOM_VICTIM. In fact I think you should try to re-use mark_oom_victim()
at least.
Oleg.
next prev parent reply other threads:[~2019-05-07 15:32 UTC|newest]
Thread overview: 113+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-10 20:34 [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android Sultan Alsawaf
2019-03-10 21:03 ` Greg Kroah-Hartman
2019-03-10 21:26 ` Sultan Alsawaf
2019-03-11 16:32 ` Joel Fernandes
2019-03-11 16:37 ` Joel Fernandes
2019-03-11 17:43 ` Michal Hocko
2019-03-11 17:58 ` Sultan Alsawaf
2019-03-11 20:10 ` Suren Baghdasaryan
2019-03-11 20:46 ` Sultan Alsawaf
2019-03-11 21:11 ` Joel Fernandes
2019-03-11 21:46 ` Sultan Alsawaf
2019-03-11 22:15 ` Suren Baghdasaryan
2019-03-11 22:36 ` Sultan Alsawaf
2019-03-12 8:05 ` Michal Hocko
2019-03-12 14:36 ` Suren Baghdasaryan
2019-03-12 15:25 ` Matthew Wilcox
2019-03-12 15:33 ` Michal Hocko
2019-03-12 15:39 ` Michal Hocko
2019-03-12 16:37 ` Sultan Alsawaf
2019-03-12 16:48 ` Michal Hocko
2019-03-12 16:58 ` Michal Hocko
2019-03-12 17:15 ` Suren Baghdasaryan
2019-03-12 17:17 ` Tim Murray
2019-03-12 17:45 ` Sultan Alsawaf
2019-03-12 18:43 ` Tim Murray
2019-03-12 18:50 ` Christian Brauner
2019-03-14 17:47 ` Joel Fernandes
2019-03-14 20:49 ` Sultan Alsawaf
2019-03-15 2:54 ` Joel Fernandes
2019-03-15 3:43 ` Sultan Alsawaf
2019-03-15 3:16 ` Steven Rostedt
2019-03-15 3:45 ` Sultan Alsawaf
2019-03-15 4:36 ` Daniel Colascione
2019-03-15 13:36 ` Joel Fernandes
2019-03-15 15:56 ` Suren Baghdasaryan
2019-03-15 16:12 ` Daniel Colascione
2019-03-15 16:43 ` Steven Rostedt
2019-03-15 17:17 ` Daniel Colascione
2019-03-15 18:03 ` Christian Brauner
2019-03-15 18:13 ` Joel Fernandes
2019-03-15 18:24 ` Christian Brauner
2019-03-15 18:49 ` Joel Fernandes
2019-03-16 17:31 ` Suren Baghdasaryan
2019-03-16 18:00 ` Daniel Colascione
2019-03-16 18:57 ` Christian Brauner
2019-03-16 19:37 ` Suren Baghdasaryan
2019-03-17 1:53 ` Joel Fernandes
2019-03-17 11:42 ` Christian Brauner
2019-03-17 15:40 ` Daniel Colascione
2019-03-18 0:29 ` Christian Brauner
2019-03-18 23:50 ` Joel Fernandes
2019-03-19 22:14 ` Christian Brauner
2019-03-19 22:26 ` Joel Fernandes
2019-03-19 22:48 ` Daniel Colascione
2019-03-19 23:10 ` Christian Brauner
2019-03-20 1:52 ` Joel Fernandes
2019-03-20 2:42 ` pidfd design Daniel Colascione
2019-03-20 3:59 ` Christian Brauner
2019-03-20 7:02 ` Daniel Colascione
2019-03-20 11:33 ` Joel Fernandes
2019-03-20 18:26 ` Christian Brauner
2019-03-20 18:38 ` Daniel Colascione
2019-03-20 18:51 ` Christian Brauner
2019-03-20 18:58 ` Andy Lutomirski
2019-03-20 19:14 ` Christian Brauner
2019-03-20 19:40 ` Daniel Colascione
2019-03-21 17:02 ` Andy Lutomirski
2019-03-25 20:13 ` Jann Horn
2019-03-25 20:23 ` Daniel Colascione
2019-03-25 23:42 ` Andy Lutomirski
2019-03-25 23:45 ` Christian Brauner
2019-03-26 0:00 ` Andy Lutomirski
2019-03-26 0:12 ` Christian Brauner
2019-03-26 0:24 ` Andy Lutomirski
2019-03-28 9:21 ` Christian Brauner
2019-03-20 19:19 ` Joel Fernandes
2019-03-20 19:29 ` Daniel Colascione
2019-03-24 14:44 ` Serge E. Hallyn
2019-03-24 18:48 ` Joel Fernandes
2019-03-20 19:11 ` Joel Fernandes
2019-05-07 2:16 ` [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android Sultan Alsawaf
2019-05-07 7:04 ` Greg Kroah-Hartman
2019-05-07 7:27 ` Sultan Alsawaf
2019-05-07 7:43 ` Greg Kroah-Hartman
2019-05-07 8:12 ` Sultan Alsawaf
2019-05-07 10:58 ` Christian Brauner
2019-05-07 16:28 ` Suren Baghdasaryan
2019-05-07 16:38 ` Christian Brauner
2019-05-07 16:53 ` Sultan Alsawaf
2019-05-07 20:01 ` Suren Baghdasaryan
2019-05-07 18:46 ` Joel Fernandes
2019-05-07 17:17 ` Sultan Alsawaf
2019-05-07 17:29 ` Greg Kroah-Hartman
2019-05-07 11:09 ` Greg Kroah-Hartman
2019-05-07 12:26 ` Michal Hocko
2019-05-07 15:31 ` Oleg Nesterov [this message]
2019-05-07 16:35 ` Sultan Alsawaf
2019-05-09 15:56 ` Oleg Nesterov
2019-05-09 18:33 ` Sultan Alsawaf
2019-05-10 15:10 ` Oleg Nesterov
2019-05-13 16:45 ` Sultan Alsawaf
2019-05-14 16:44 ` Steven Rostedt
2019-05-14 17:31 ` Sultan Alsawaf
2019-05-15 14:58 ` Oleg Nesterov
2019-05-15 17:27 ` Sultan Alsawaf
2019-05-15 18:32 ` Steven Rostedt
2019-05-15 18:52 ` Sultan Alsawaf
2019-05-15 20:09 ` Steven Rostedt
2019-05-16 13:54 ` Oleg Nesterov
2019-03-17 16:35 ` Serge E. Hallyn
2019-03-17 17:11 ` Daniel Colascione
2019-03-17 17:16 ` Serge E. Hallyn
2019-03-17 22:02 ` Suren Baghdasaryan
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