On Sun, Sep 24, 2017 at 1:08 PM, Alexey Dobriyan <adobri...@gmail.com> wrote: > From: Tatsiana Brouka <tatsiana_bro...@epam.com> > > Implement system call for bulk retrieveing of pids in binary form. > > Using /proc is slower than necessary: 3 syscalls + another 3 for each thread + > converting with atoi() + instantiating dentries and inodes. > > /proc may be not mounted especially in containers. Natural extension of > hidepid=2 efforts is to not mount /proc at all. > > It could be used by programs like ps, top or CRIU. Speed increase will > become more drastic once combined with bulk retrieval of process statistics. > > Benchmark: > > N=1<<16 times > ~130 processes (~250 task_structs) on a regular desktop system > opendir + readdir + closedir /proc + the same for every > /proc/$PID/task > (roughly what htop(1) does) vs pidmap > > /proc 16.80 ± 0.73% > pidmap 0.06 ± 0.31% > > PIDMAP_* flags are modelled after /proc/task_diag patchset. > > > PIDMAP(2) Linux Programmer's Manual PIDMAP(2) > > NAME > pidmap - get allocated PIDs > > SYNOPSIS > long pidmap(pid_t pid, int *pids, unsigned int count , unsigned int > start, int flags);
I think we will seriously regret a syscall that does this. Djalal is working on fixing the turd that is hidepid, and this syscall is basically incompatible with ever fixing hidepids. I think that, to make it less regrettable, it needs to take an fd to a proc mount as a parameter. This makes me wonder why it's a syscall at all -- why not just create a new file like /proc/pids? --Andy
