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

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Message-ID: <20141023123855.GC12706@worktop.programming.kicks-ass.net>
Date:	Thu, 23 Oct 2014 14:38:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	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, acme@...radead.org
Subject: Re: [PATCH v5 18/20] perf: Allocate ring buffers for inherited
 per-task kernel events

On Mon, Oct 13, 2014 at 04:45:46PM +0300, Alexander Shishkin wrote:
> Normally, per-task events can't be inherited parents' ring buffers to
> avoid multiple events contending for the same buffer. And since buffer
> allocation is typically done by the userspace consumer, there is no
> practical interface to allocate new buffers for inherited counters.
> 
> However, for kernel users we can allocate new buffers for inherited
> events as soon as they are created (and also reap them on event
> destruction). This pattern has a number of use cases, such as event
> sample annotation and process core dump annotation.
> 
> 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.
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