From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752171Ab1KYQog (ORCPT ); Fri, 25 Nov 2011 11:44:36 -0500 Received: from mailhub.sw.ru ([195.214.232.25]:48322 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751029Ab1KYQof (ORCPT ); Fri, 25 Nov 2011 11:44:35 -0500 Message-ID: <4ECFC5E3.5090900@parallels.com> Date: Fri, 25 Nov 2011 20:44:19 +0400 From: Pavel Emelyanov User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 MIME-Version: 1.0 To: Oleg Nesterov CC: Tejun Heo , Pedro Alves , Linux Kernel Mailing List , Cyrill Gorcunov , James Bottomley Subject: Re: [RFC][PATCH 0/3] fork: Add the ability to create tasks with given pids References: <4EC4F2FB.408@parallels.com> <201111221204.39235.pedro@codesourcery.com> <20111122153326.GD322@google.com> <201111231620.45440.pedro@codesourcery.com> <20111123162417.GE25780@google.com> <4ECD3946.1030503@parallels.com> <4ECD542C.7010705@parallels.com> <20111124173121.GA23260@redhat.com> <4ECF6AA0.80006@parallels.com> <20111125162220.GA17173@redhat.com> In-Reply-To: <20111125162220.GA17173@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/25/2011 08:22 PM, Oleg Nesterov wrote: > On 11/25, Pavel Emelyanov wrote: >> >> The proposal is to implement the PR_RESERVE_PID prctl which allocates and puts a >> pid on the current. The subsequent fork() uses this pid, > > Oh. This is subjective, yes, but this doesn't clean to me. > > Amd why?? On the running system PR_RESERVE_PID can obviously fail anyway. > It only helps to avoid the race with another fork. No. It can fail if you try to allocate a pid with given number. The API allows for pid generation. AFAIU this can help with Pedro's requirements to resurrect task with the same pid value it used to have before. >> * one more field on struct pid is OK, since it size doesn't change (32 bit level is >> anyway not required, it's OK to reduce on down to 16 bits) > > Even if sizeof is the same, the new member and the code which plays > with ->flags doesn't make the things better ;) > >> * yes, we have +1 member on task_struct :( > > Yes, and this task_struct->rsv_pid acts as implicit parameter for the > next clone(). Doesn't look very nice to me. Plus the code complications. Well, the last_pid is also an implicit parameter for the next clone() with sysctl approach :) But the code complication is the problem, yes :( >> Oleg, Tejun, do you agree with such an approach? > > If set_last_pid doesn't work, I'd prefer CLONE_CHILD_USEPIDS. OK, thanks. > Oleg. > > . >