linux-kernel - Re: [PATCH v5 18/20] perf: Allocate ring buffers for inherited per-task kernel events

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Date:	Thu, 30 Oct 2014 11:31:00 -0200
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com
Subject: Re: [PATCH v5 18/20] perf: Allocate ring buffers for inherited
 per-task kernel events

Em Thu, Oct 30, 2014 at 09:43:59AM +0100, Peter Zijlstra escreveu:
> On Fri, Oct 24, 2014 at 10:44:54AM +0300, Alexander Shishkin wrote:
> > Peter Zijlstra <peterz@...radead.org> writes:
> > > On Mon, Oct 13, 2014 at 04:45:46PM +0300, Alexander Shishkin wrote:
> > >> When a new event is inherited from a per-task kernel event that has a
> > >> ring buffer, allocate a new buffer for this event so that data from the
> > >> child task is collected and can later be retrieved for sample annotation
> > >> or core dump inclusion. This ring buffer is released when the event is
> > >> freed, for example, when the child task exits.

> > > This causes a pinned memory explosion, not at all nice that.

> > > I think I see why and all, but it would be ever so good to not have to
> > > allocate so much memory.

> > Are there any controls we could use to limit such memory usage?

> I'd say the same limit we're already accounting the mmap()s against. But
> the question is; what do we do when we run out?

> Will we fail clone()? That might 'surprise' quite a few people, that

> their application won't work when profiled.

Can't we just emit PERF_RECORD_THROTTLE or similar stuff then? I.e.
somehow mark the cloned process as not being profiled due to ENOMEM?

- Arnaldo
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