Default buffer size of getcwd for linux

[inteon]

It seems like, by default, the initial buffer size for the return value of getcwd is set to 512 bytes:

rust/library/std/src/sys/unix/os.rs

Line 139 in 600820d

let mut buf = Vec::with_capacity(512);

The default in glibc is defined as follows (https://code.woboq.org/userspace/glibc/sysdeps/unix/sysv/linux/getcwd.c.html#61):

MAX (PATH_MAX, __getpagesize ())

This might cause some unnecessary linux kernel context switches for longer paths (multiple buffer resizes).
Is there a reason for not using a larger buffer (eg. identical to the glibc implementation)?

[the8472]

This should only make a difference for code that calls it in a loop, does that happen somewhere where it's not easily fixed?

[inteon]

ref: denoland/deno#12056

Also, I'm asking this question out of curiosity, what is the main reason for the 512 bytes value?
It seems like most implementations use the PATH_MAX value, eg. Golang uses Getwd (https://go.dev/src/os/getwd.go).

[the8472]

See the discussion in #27930 which originally implemented it.

[inteon]

See the discussion in #27930 which originally implemented it.

Thank you for the info, I'll do some further testing & create a PR in case I find something valuable.