fix: speed up fd closing on Linux #54
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On some AWS/container Linux environments `RLIMIT_NOFILE` (and therefore `sysconf(_SC_OPEN_MAX)`) can be set extremely high (e.g. 1,048,576). Exile’s spawner was closing non-stdio fds by looping from 3.._SC_OPEN_MAX, which turns each spawn into ~1M `close()` syscalls and can add seconds of overhead even for trivial commands. Fix this on Linux by: - Trying `close_range(2)` (Linux 5.9+) via `syscall()` to efficiently close all fds >= 3 in the kernel. - Falling back to scanning `/proc/self/fd` and closing only the fds that are actually open (O(open_fds)). - If both approaches fail, fall back to the historical close-loop. Non-Linux platforms keep the existing behavior unchanged.
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@davidjulien Thank you very much for investigating the issue and finding a fix! 👍🏼 I'll review and cut a release soon, within next few days. |
Owner
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@davidjulien Thanks for the PR and your patience! On closer inspection, we don't actually need to iterate through all FDs. The BEAM already ensures that no unrelated file descriptors survive the exec by using FD_CLOEXEC on all internally managed descriptors. See: https://github.com/erlang/otp/blob/master/erts/emulator/sys/unix/erl_child_setup.c#L310-L315 #55 addresses the issue differently. Closing the PR. |
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On some AWS/container Linux environments
RLIMIT_NOFILE(and thereforesysconf(_SC_OPEN_MAX)) can be set extremely high (e.g. 1,048,576). Exile’s spawner was closing non-stdio fds by looping from 3.._SC_OPEN_MAX, which turns each spawn into ~1Mclose()syscalls and can add seconds of overhead even for trivial commands.Fix this on Linux by:
close_range(2)(Linux 5.9+) viasyscall()to efficiently close all fds >= 3 in the kernel./proc/self/fdand closing only the fds that are actually open (O(open_fds)).Non-Linux platforms keep the existing behavior unchanged.