On Tue, Sep 26, 2017 at 11:46 AM, Alexey Dobriyan <[email protected]> wrote: > On Sun, Sep 24, 2017 at 02:27:00PM -0700, Andy Lutomirski wrote: >> On Sun, Sep 24, 2017 at 1:08 PM, Alexey Dobriyan <[email protected]> wrote: >> > From: Tatsiana Brouka <[email protected]> >> > >> > 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 ą 0.73% >> > pidmap 0.06 ą 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.
Your syscall cannot be implemented sanely. It doesn't remove bullshit -- it adds bullshit. NAK.
