Messages in this thread | | | Date | Thu, 30 Oct 2014 09:43:59 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5 18/20] perf: Allocate ring buffers for inherited per-task kernel events |
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On Fri, Oct 24, 2014 at 10:44:54AM +0300, Alexander Shishkin wrote: > Peter Zijlstra <peterz@infradead.org> writes: > > > 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. > > 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.
In any case, lets focus on the other parts of this work and delay this feature till later.
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