On Sun, Sep 24, 2017 at 02:27:00PM -0700, Andy Lutomirski wrote: > 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?
See reply to fdmap(2). pidmap(2) is indeed more complex case exactly because of pid/tgid/tid/everything else + pidnamespaces + ->hide_pid. However the problem remains: query task tree without all the bullshit. C/R people succumbed with /proc/*/children, it was a mistake IMO.
