From: Sultan Alsawaf <sultan@kerneltoast.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: "Tim Murray" <timmurray@google.com>,
"Michal Hocko" <mhocko@kernel.org>,
"Suren Baghdasaryan" <surenb@google.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Arve Hjønnevåg" <arve@android.com>,
"Todd Kjos" <tkjos@android.com>,
"Martijn Coenen" <maco@android.com>,
"Christian Brauner" <christian@brauner.io>,
"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>,
"Steven Rostedt" <rostedt@goodmis.org>
Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android
Date: Thu, 14 Mar 2019 13:49:11 -0700 [thread overview]
Message-ID: <20190314204911.GA875@sultan-box.localdomain> (raw)
In-Reply-To: <CAEXW_YQMnbN+e-janGbZc5MH6MwdUdXNfonpLUu5O2nsSkJyeg@mail.gmail.com>
On Thu, Mar 14, 2019 at 10:47:17AM -0700, Joel Fernandes wrote:
> About the 100ms latency, I wonder whether it is that high because of
> the way Android's lmkd is observing that a process has died. There is
> a gap between when a process memory is freed and when it disappears
> from the process-table. Once a process is SIGKILLed, it becomes a
> zombie. Its memory is freed instantly during the SIGKILL delivery (I
> traced this so that's how I know), but until it is reaped by its
> parent thread, it will still exist in /proc/<pid> . So if testing the
> existence of /proc/<pid> is how Android is observing that the process
> died, then there can be a large latency where it takes a very long
> time for the parent to actually reap the child way after its memory
> was long freed. A quicker way to know if a process's memory is freed
> before it is reaped could be to read back /proc/<pid>/maps in
> userspace of the victim <pid>, and that file will be empty for zombie
> processes. So then one does not need wait for the parent to reap it. I
> wonder how much of that 100ms you mentioned is actually the "Waiting
> while Parent is reaping the child", than "memory freeing time". So
> yeah for this second problem, the procfds work will help.
>
> By the way another approach that can provide a quick and asynchronous
> notification of when the process memory is freed, is to monitor
> sched_process_exit trace event using eBPF. You can tell eBPF the PID
> that you want to monitor before the SIGKILL. As soon as the process
> dies and its memory is freed, the eBPF program can send a notification
> to user space (using the perf_events polling infra). The
> sched_process_exit fires just after the mmput() happens so it is quite
> close to when the memory is reclaimed. This also doesn't need any
> kernel changes. I could come up with a prototype for this and
> benchmark it on Android, if you want. Just let me know.
Perhaps I'm missing something, but if you want to know when a process has died
after sending a SIGKILL to it, then why not just make the SIGKILL optionally
block until the process has died completely? It'd be rather trivial to just
store a pointer to an onstack completion inside the victim process' task_struct,
and then complete it in free_task().
Thanks,
Sultan
next prev parent reply other threads:[~2019-03-14 20:49 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 [this message]
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
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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