https://issues.dlang.org/show_bug.cgi?id=14770
Issue ID: 14770
Summary: std.process should use lightweight forks where
available
Product: D
Version: D2
Hardware: x86_64
OS: All
Status: NEW
Severity: normal
Priority: P1
Component: phobos
Assignee: [email protected]
Reporter: [email protected]
fork(even with CoW pages) can be extremely slow with modern memory usages due
to the antiquated default page size of OSes because it requires copying the
page table.
For example, a program using 400MiB of memory with 4KiB pages requires copying
102,400 page structs. On Linux, a page struct in the kernel is at least 72
bytes so this requires a copy of 7.2MiB.
This scales linearly with heap size, after some personal testing on Linux I
found forking with almost nothing allocated to take ~60 microseconds, 100 MiB
~3 milliseconds, and 1GiB to take 30-45 milliseconds. vfork took a constant 20
microseconds no matter the heap size.
Solution: where available, use posix_spawn, vfork, etc. These do not require
copying page tables. std.process does not require the page tables since it
immediately replaces itself with another process.
I marked this all OSes, but really it's all POSIX OSes I guess.
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