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

[Peter Zijlstra]

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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