Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932317AbbGGQYe (ORCPT ); Tue, 7 Jul 2015 12:24:34 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:33553 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757386AbbGGQY0 (ORCPT ); Tue, 7 Jul 2015 12:24:26 -0400 MIME-Version: 1.0 In-Reply-To: <559BFB9C.5010801@gmail.com> References: <1436172445-6979-1-git-send-email-avagin@openvz.org> <20150707154345.GA1593@odin.com> <559BFB9C.5010801@gmail.com> From: Andy Lutomirski Date: Tue, 7 Jul 2015 09:24:05 -0700 Message-ID: Subject: Re: [PATCH 0/24] kernel: add a netlink interface to get information about processes (v2) To: David Ahern Cc: Andrew Vagin , Andrey Vagin , "linux-kernel@vger.kernel.org" , Linux API , Oleg Nesterov , Andrew Morton , Cyrill Gorcunov , Pavel Emelyanov , Roger Luethi , Arnd Bergmann , Arnaldo Carvalho de Melo , Pavel Odintsov Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1623 Lines: 35 On Tue, Jul 7, 2015 at 9:17 AM, David Ahern wrote: > On 7/7/15 9:56 AM, Andy Lutomirski wrote: >> >> Netlink is fine for these use cases (if they were related to the >> netns, not the pid ns or user ns), and it works. It's still tedious >> -- I bet that if you used a syscall, the user code would be >> considerable shorter, though. :) >> >> How would this be a problem if you used plain syscalls? The user >> would make a request, and the syscall would tell the user that their >> result buffer was too small if it was, in fact, too small. > > > It will be impossible to tell a user what sized buffer is needed. The size > is largely a function of the number of tasks and number of maps per thread > group and both of those will be changing. With the growing size of systems > (I was sparc systems with 1024 cpus) the workload can be 10's of thousands > of tasks each with a lot of maps (e.g., java workloads). That amounts to a > non-trivial amount of data that has to be pushed to userspace. > > One of the benefits of the netlink approach is breaking the data across > multiple messages and picking up where you left off. That infrastructure is > already in place. > How does picking up where you left off work? I assumed the interface was something along the lines of "give me information starting from pid N", but maybe I missed something. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/