From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02400C33CB3 for ; Tue, 14 Jan 2020 08:40:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCD4D217BA for ; Tue, 14 Jan 2020 08:40:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728721AbgANIkB (ORCPT ); Tue, 14 Jan 2020 03:40:01 -0500 Received: from relay.sw.ru ([185.231.240.75]:53820 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727083AbgANIkA (ORCPT ); Tue, 14 Jan 2020 03:40:00 -0500 Received: from dhcp-172-16-24-104.sw.ru ([172.16.24.104]) by relay.sw.ru with esmtp (Exim 4.92.3) (envelope-from ) id 1irHjU-0005aa-Ob; Tue, 14 Jan 2020 11:39:29 +0300 Subject: Re: [PATCH 2/4] mm: introduce external memory hinting API To: Daniel Colascione Cc: Minchan Kim , Andrew Morton , LKML , linux-mm , Linux API , oleksandr@redhat.com, Suren Baghdasaryan , Tim Murray , Sandeep Patil , Sonny Rao , Brian Geffon , Michal Hocko , Johannes Weiner , Shakeel Butt , John Dias References: <20200110213433.94739-1-minchan@kernel.org> <20200110213433.94739-3-minchan@kernel.org> <56ea0927-ad2e-3fbd-3366-3813330f6cec@virtuozzo.com> From: Kirill Tkhai Message-ID: <3eec2097-75a3-1e1d-06d9-44ee5eaf1312@virtuozzo.com> Date: Tue, 14 Jan 2020 11:39:28 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13.01.2020 22:18, Daniel Colascione wrote: > On Mon, Jan 13, 2020, 12:47 AM Kirill Tkhai wrote: >>> +SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start, >>> + size_t, len_in, int, behavior, unsigned long, flags) >> >> I don't like the interface. The fact we have pidfd does not mean, >> we have to use it for new syscalls always. A user may want to set >> madvise for specific pid from console and pass pid as argument. >> pidfd would be an overkill in this case. >> We usually call "kill -9 pid" from console. Why shouldn't process_madvise() >> allow this? > > All new APIs should use pidfds: they're better than numeric PIDs Yes > in every way. No > If a program wants to allow users to specify processes by > numeric PID, it can parse that numeric PID, open the corresponding > pidfd, and then use that pidfd with whatever system call it wants. > It's not necessary to support numeric PIDs at the system call level to > allow a console program to identify a process by numeric PID. No. It is overkill. Ordinary pid interfaces also should be available. There are a lot of cases, when they are more comfortable. Say, a calling of process_madvise() from tracer, when a tracee is stopped. In this moment the tracer knows everything about tracee state, and pidfd brackets pidfd_open() and close() around actual action look just stupid, and this is cpu time wasting. Another example is a parent task, which manages parameters of its children. It knows everything about them, whether they are alive or not. Pidfd interface will just utilize additional cpu time here. So, no. Both interfaces should be available.