On Wed, Sep 6, 2017 at 2:04 AM, Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote: > On 9/6/17, Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote: >> On 09/05/17 15:53, Andrew Morton wrote: >>> On Tue, 5 Sep 2017 22:05:00 +0300 Alexey Dobriyan <adobriyan@xxxxxxxxx> >>> wrote: >>> >>>> 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(). >>>> >>>> /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. >>> >>> The patches are performance optimizations, but their changelogs contain >>> no performance measurements! >>> >>> Demonstration of some compelling real-world performance benefits would >>> help things along a lot. >>> >> >> also, I expect that the tiny kernel people will want kconfig options for >> these syscalls. > > We'll add it but the question if it is a good idea. Ideally these system calls > should be mandatory and /proc optional. > > $ size kernel/pidmap.o fs/fdmap.o > text data bss dec hex filename > 560 0 0 560 230 kernel/pidmap.o > 617 0 0 617 269 fs/fdmap.o After much discussion at LPC/KS last year, I thought the idea was to try to speed up /proc rather than replacing it outright. The two specific ideas I recall were: 1. Add a syscall like readfileat() that you can use to, in a single operation, open, read, and close a /proc file (or other file). This should vastly reduce locking and RCU overhead. 2. Add a /proc file that has a nice binary format for task info. (nl_attr?) I don't see why pidmap() deserves to be significantly faster than getdents(). Also, a pidmap() syscall like this inherently bypasses any security restrictions implied by the way that /proc is mounted. It can respect hidepid, but hidepid (as a per-namespace concept) is an enormous turd that badly needs to be deprecated, and Djalal is working on exactly that. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
