netdev - Re: [PATCH bpf-next 2/3] bpf: emit RECORD_MMAP events for bpf prog load/unload

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Date:   Thu, 20 Sep 2018 15:56:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        "David S . Miller" <davem@...emloft.net>, daniel@...earbox.net,
        netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 2/3] bpf: emit RECORD_MMAP events for bpf prog
 load/unload

On Thu, Sep 20, 2018 at 10:25:45AM -0300, Arnaldo Carvalho de Melo wrote:
> PeterZ provided a patch introducing PERF_RECORD_MUNMAP, went nowhere due
> to having to cope with munmapping parts of existing mmaps, etc.
> 
> I'm still more in favour of introduce PERF_RECORD_MUNMAP, even if for
> now it would be used just in this clean case for undoing a
> PERF_RECORD_MMAP for a BPF program.
> 
> The ABI is already complicated, starting to use something called
> PERF_RECORD_MMAP for unmmaping by just using a NULL name... too clever,
> I think.

Agreed, the PERF_RECORD_MUNMAP patch was fairly trivial, the difficult
part was getting the perf tool to dtrt for that use-case. But if we need
unmap events, doing the unmap record now is the right thing.