[PATCH 0/3] perf: builtin-record: Be more helpful when running up against mlock limits.

[Nelson Elhage]

With the current code, it's relatively easy to run up against the
perf_event_mlock_kb limit if you try to attach to a multithreaded
target with 'perf record -p', because perf will attempt to mmap 512k
per target thread, and the default mlock limit is (512k + 1 page),
total.

Current, this results in a completely inscrutable
  Fatal: failed to mmap with 22 (Invalid argument)

We should perhaps automatically detect a better choice of mmap_pages,
but in the meanwhile, it's easy to improve the error to give users
some guidance about what's going on, so that hopefully I can be the
last person to have to source-dive to figure out what's going on.

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