From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Anton Blanchard <anton@ozlabs.org>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 2/2] trace/kprobe: Remove limit on kretprobe maxactive
Date: Tue, 15 Jun 2021 23:11:27 +0530 [thread overview]
Message-ID: <1623777582.jsiokbdey1.naveen@linux.ibm.com> (raw)
In-Reply-To: <20210615183527.9068ef2f70fdd2a45fea78f0@kernel.org>
Masami Hiramatsu wrote:
> On Mon, 14 Jun 2021 23:33:29 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>
>> We currently limit maxactive for a kretprobe to 4096 when registering
>> the same through tracefs. The comment indicates that this is done so as
>> to keep list traversal reasonable. However, we don't ever iterate over
>> all kretprobe_instance structures. The core kprobes infrastructure also
>> imposes no such limitation.
>>
>> Remove the limit from the tracefs interface. This limit is easy to hit
>> on large cpu machines when tracing functions that can sleep.
>>
>> Reported-by: Anton Blanchard <anton@ozlabs.org>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>
> OK, but I don't like to just remove the limit (since it can cause
> memory shortage easily.)
> Can't we make it configurable? I don't mean Kconfig, but
> tracefs/options/kretprobe_maxactive, or kprobes's debugfs knob.
>
> Hmm, maybe debugfs/kprobes/kretprobe_maxactive will be better since
> it can limit both trace_kprobe and kprobes itself.
I don't think it is good to put a new tunable in debugfs -- we don't
have any kprobes tunable there, so this adds a dependency on debugfs
which shouldn't be necessary.
/proc/sys/debug/ may be a better fit since we have the
kprobes-optimization flag to disable optprobes there, though I'm not
sure if a new sysfs file is agreeable.
But, I'm not too sure this really is a problem. Maxactive is a user
_opt-in_ feature which needs to be explicitly added to an event
definition. In that sense, isn't this already a tunable?
- Naveen
next prev parent reply other threads:[~2021-06-15 17:42 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-14 18:03 [PATCH 0/2] trace/kprobe: Two fixes for kretprobes Naveen N. Rao
2021-06-14 18:03 ` [PATCH 1/2] trace/kprobe: Fix count of missed kretprobes in kprobe_profile Naveen N. Rao
2021-06-15 5:47 ` Masami Hiramatsu
2021-06-14 18:03 ` [PATCH 2/2] trace/kprobe: Remove limit on kretprobe maxactive Naveen N. Rao
2021-06-15 9:35 ` Masami Hiramatsu
2021-06-15 17:41 ` Naveen N. Rao [this message]
2021-06-16 0:46 ` Masami Hiramatsu
2021-06-16 1:03 ` Steven Rostedt
2021-06-16 2:27 ` Masami Hiramatsu
2021-06-16 15:10 ` Masami Hiramatsu
2021-06-17 16:34 ` Naveen N. Rao
2021-06-17 17:07 ` Steven Rostedt
2021-06-18 4:26 ` Masami Hiramatsu
2021-06-18 8:41 ` Naveen N. Rao
2021-06-17 16:19 ` Naveen N. Rao
2021-06-18 6:17 ` Masami Hiramatsu
2021-06-18 13:19 ` Naveen N. Rao
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