[systemd-devel] Significant performance loss caused by commit a65f06b: journal: return -ECHILD after a fork

[Florian Weimer]

* Lennart Poettering:

> On Tue, 11.07.17 21:26, Florian Weimer (fw at deneb.enyo.de) wrote:
>
>> * Lennart Poettering:
>> 
>> > Apparently, this regressed between this version and
>> > glibc-2.24-9.fc25.x86_64 hence.
>> 
>> Yes, I backported the fork cache removal to Fedora 25.  There is no
>> longer a good way to main such a cache in userspace because glibc
>> cannot intercept anymore all the ways that can change the PID of the
>> current process because the kernel interfaces for process management
>> are incredibly rich these days.
>
> BTW, with this change you are breaking expressly documented behaviour:
>
> http://man7.org/linux/man-pages/man2/getpid.2.html
>
>     "Since glibc version 2.3.4, the glibc wrapper function for
>      getpid() caches PIDs, so as to avoid additional system calls when
>      a process calls getpid() repeatedly."

Note that the manpages project, while extremely valuable, is not
official glibc documentation and sometimes explains library internals
which can change over time.