From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757066AbZHHBl0 (ORCPT ); Fri, 7 Aug 2009 21:41:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754774AbZHHBlZ (ORCPT ); Fri, 7 Aug 2009 21:41:25 -0400 Received: from smtp-out.google.com ([216.239.45.13]:44782 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754602AbZHHBlY (ORCPT ); Fri, 7 Aug 2009 21:41:24 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: cc:content-type:content-transfer-encoding:x-system-of-record; b=wvMieU2lA/FfkQqKaHT81IgIdbrPhGtdTr61l0PnxXn1dGWLa2wDSY/KHUWhJMQWR GCJ9UblMJV0xEBBfgjrYQ== MIME-Version: 1.0 In-Reply-To: <6599ad830908060440g2f6cbed6xdc54c7096cd3745e@mail.gmail.com> References: <20090803194555.GA10158@us.ibm.com> <6599ad830908041228w67bc6f7fh57e28f244e1923b3@mail.gmail.com> <20090805102057.GT29252@hawkmoon.kerlabs.com> <6599ad830908050911t6f23f810i65fe8fe17f3ee698@mail.gmail.com> <20090805164218.GB26446@hawkmoon.kerlabs.com> <2f86c2480908051701s57120404q475edbedb58cdca1@mail.gmail.com> <20090806095854.GD26446@hawkmoon.kerlabs.com> <6599ad830908060328y21a008c1pc5ed5c27e0ec905d@mail.gmail.com> <20090806112450.GF26446@hawkmoon.kerlabs.com> <6599ad830908060440g2f6cbed6xdc54c7096cd3745e@mail.gmail.com> Date: Fri, 7 Aug 2009 18:41:21 -0700 Message-ID: <2f86c2480908071841h13009856hd8fcae167b1fadbf@mail.gmail.com> Subject: Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once From: Benjamin Blum To: Paul Menage Cc: containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Peter Zijlstra Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 6, 2009 at 4:40 AM, Paul Menage wrote: > On Thu, Aug 6, 2009 at 4:24 AM, Louis Rilling wrote: >> >> You meant signal_struct, right? sighand_struct can be shared by several >> thread groups, while signal_struct can't. >> > > No, I meant sighand_struct. I realise that it *can* be shared between > processes, but I didn't think that NPTL actually did so. (Are there > common cases of this happening?) And in cases where it was shared, it > wouldn't affect correctness, but simply create the potential for a > little more contention. > > I agree that signal_struct might in principle be a better place for > it, but the first cacheline of signal_struct appears to be occupied > with performance-sensitive things (a couple of counters and a queue > used in do_wait()) already, whereas the first cacheline of > sighand_struct only appears to be used incremented/decremented during > fork/exit, and when delivering a bunch of mostly-fatal signals. > > But having said that, if having it in signal_struct isn't considered a > potential performance hit, it would be fine there too. > > Paul > I'm presently rewriting the locking scheme here to have the rwsem live in sighand_struct, and writing two new functions lock_threadgroup_fork and unlock_threadgroup_fork (for use in cgroup_attach_proc) which will live in cgroup.c but are generic enough that they could be used by anybody who wants to do threadgroup-wide fork-sensitive changes. I'm also having the fork_lock under an #ifdef CONFIG_CGROUPS, which could be expanded to, say, CONFIG_FORK_LOCK_THREADGROUP (which CGROUPS would depend upon) if somebody else ever wanted to use this lock as well. For genericness, I'll have the down_read and up_read on the lock in do_fork() directly (instead of cgroup_fork and cgroup_post_fork as it is in this version of the patch). If there are no more comments/discussion on the locking scheme, I'll resubmit the patch series with these changes approximately Monday.