Re: [RFC] perf: mmap2 not covering VM_CLONE regions

[David Ahern <dsahern@gmail.com>]

On 10/8/13 1:54 PM, Stephane Eranian wrote:
>>> If the current MMAP2 is not a complete solution for what you (Google)
>>> need, should support be reverted before 3.12 is released? No sense in
>>> making this part of the forever API if more work is needed on it.
>>
>> Instead of a full revert we could just turn off the ABI portion minimally
>> and not recognize it for now. Assuming a more complete solution is in the
>> works for v3.13.
>>
> That's a possibility. They are also pieces in the perf tool itself.
> We could certainly make the attr->mmap2 bit disappear.
>
> I think it boils down to how can we uniquely identify virtual
> mapping to the same physical data either via shmat(), files, VM_CLONE.
> We had all covered but the last case with the ino approach. We don't have
> a solution for VM_CLONE yet.
>

I was mainly thinking the 2 parts that generate MMAP2 events: kernel 
side it's the mmap2 attribute and perf_event_mmap_output; userspace side 
it's perf_event__synthesize_mmap_event. Certainly the rest of the 
plumbing can be left in place until the solution is refined as needed.

David