[issue1572968] release GIL while doing I/O operations in the mmap module

[Nic Watson]

Nic Watson <pythonbugs at nicwatson.org> added the comment:

I'll add one more system I/O call that's not GIL-wrapped in the mmap module that can take some time:  mmap itself.

mmap on Linux with MAP_POPULATE (0x8000) as the flags can take quite a bit of time.  That's the flag that prefaults the memory range.  MAP_POPULATE has been around since Linux 2.5.46.

I know that MAP_POPULATE isn't explicitly supported in the module, but mmap.mmap does take arbitrary flags, so it isn't exactly unsupported either.

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nosy: +jnwatson

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