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

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On Fri, Sep 23, 2016 at 02:27:21PM +0300, Alexander Shishkin wrote:
> In order to be able to allocate perf ring buffers in non-mmap path, we
> need to make sure we can still account the memory to the user and that
> they don't exceed their mlock limit.
> 
> This patch moves ring buffer memory accounting down the rb_alloc() path
> so that its callers won't have to worry about it. This also serves the
> additional purpose of slightly cleaning up perf_mmap().

While I like a cleanup of that code (it really can use one), I'm not a
big fan of hidden buffers like this. Why is this needed?

A quick look through the patches also leaves me wondering on the design
and interface of this thing. A few words explaining the overall design
would be nice.

Afaict there's no actual need to hide the AUX buffer for this sampling
stuff; the user knows about all this and can simply mmap() the AUX part.
The sample could either point to locations in the AUX buffer, or (as I
think this code does) memcpy bits out.

Ideally we'd pass the AUX-event into the syscall, that way you avoid all
the find_aux_event crud. I'm not sure we want to overload the group_fd
thing more (its already very hard to create counter groups in a cgroup
for example) ..

Coredump was mentioned somewhere, but I'm not sure I've seen
code/interfaces for that. How was that envisioned to work?

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[RFC PATCH 0/6] perf: Add AUX data sampling Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 13:30 +0200
  [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 13:30 +0200
    Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer  allocation Peter Zijlstra <peterz@infradead.org> - 2016-09-23 14:20 +0200
      Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 16:40 +0200
        Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer  allocation Peter Zijlstra <peterz@infradead.org> - 2016-09-23 17:30 +0200
          Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 18:00 +0200
      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
  [RFC PATCH 2/6] perf: Add api to (de-)allocate AUX buffers for kernel counters Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 13:40 +0200
  [RFC PATCH 3/6] perf: Add a helper for looking up pmus by type Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 13:40 +0200
  [RFC PATCH 4/6] perf: Add infrastructure for using AUX data in perf samples Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 13:40 +0200
  [RFC PATCH 5/6] perf: Disable PMU around address filter adjustment Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 13:40 +0200
  [RFC PATCH 6/6] perf: Disable IRQs in address filter sync path Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-23 13:40 +0200
    Re: [RFC PATCH 6/6] perf: Disable IRQs in address filter sync path Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-26 18:30 +0200
      Re: [RFC PATCH 6/6] perf: Disable IRQs in address filter sync path Mathieu Poirier <mathieu.poirier@linaro.org> - 2016-10-04 18:50 +0200
  Re: [RFC PATCH 0/6] perf: Add AUX data sampling Peter Zijlstra <peterz@infradead.org> - 2016-09-23 13:50 +0200
    Re: [RFC PATCH 0/6] perf: Add AUX data sampling Andi Kleen <ak@linux.intel.com> - 2016-09-23 19:20 +0200
      Re: [RFC PATCH 0/6] perf: Add AUX data sampling Peter Zijlstra <peterz@infradead.org> - 2016-09-23 22:40 +0200
        Re: [RFC PATCH 0/6] perf: Add AUX data sampling Andi Kleen <ak@linux.intel.com> - 2016-09-24 00:40 +0200

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