Messages in this thread | | | Date | Fri, 23 Sep 2016 14:14:03 +0200 | From | Peter Zijlstra <> | Subject | 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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