Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation

From	Alexander Shishkin <alexander.shishkin@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation
Date	2016-09-26 14:50 +0200
Message-ID	<slDw5-3SS-19@gated-at.bofh.it> (permalink)
References	(2 earlier) <skxCq-3yR-33@gated-at.bofh.it> <skCsp-6Lq-15@gated-at.bofh.it> <skFgC-8uY-13@gated-at.bofh.it> <slzst-1vb-13@gated-at.bofh.it> <slA5b-1Xk-13@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Peter Zijlstra <peterz@infradead.org> writes:

> On Mon, Sep 26, 2016 at 11:27:08AM +0300, Alexander Shishkin wrote:
>> Peter Zijlstra <peterz@infradead.org> writes:
>> > At which point we _should_ start failing fork(), which is a somewhat
>> > unexpected, and undesirable side-effect.
>> 
>> I'm not sure I see why we should fail fork() when we run out of pinned
>> memory.
>
> Well, we cannot fully honour the inherit, what other option do we have?
> Silently malfunctioning? That's far worse.

We can still put a note there saying that we tried. The user will know
to adjust their buffer size requirement or the RLIMIT_MEMLOCK.

>> > Ideally we'd unpin the old buffers and repin the new buffers on context
>> > switch, but that's impossible since faulting needs scheduling,
>> > recursion, we loose.
>> 
>> Or we can have per-cpu buffers for all user's tasks, record where each
>> task starts and ends in each buffer and cut out only bits relevant to
>> the task(s) that dump core.
>
> Which gets you the problem that when a task dumps core there might not
> be any state in the buffer, because the previous task flushed it all out
> :/

Well, there's going to be at list something that leads up to the core
dump if this task is the last one to schedule in for this buffer. It's a
bit more gambling, though.

Regards,
--
Alex

Thread

Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer  allocation Andi Kleen <ak@linux.intel.com> - 2016-09-23 19:30 +0200
  Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer  allocation Peter Zijlstra <peterz@infradead.org> - 2016-09-23 22:30 +0200
    Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-26 10:30 +0200
      Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer  allocation Peter Zijlstra <peterz@infradead.org> - 2016-09-26 11:10 +0200
        Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-26 14:50 +0200
        Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-26 18:20 +0200

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