From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH 2/4] Convert epoll to a bitlock Date: Tue, 03 Feb 2009 22:55:26 +0100 Message-ID: <4988BD4E.8080206@cosmosbay.com> References: <1233598811-6871-1-git-send-email-corbet@lwn.net> <1233598811-6871-3-git-send-email-corbet@lwn.net> <20090203133942.2ecec281.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20090203133942.2ecec281.akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrew Morton Cc: Jonathan Corbet , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org, oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org, davidel-AhlLAIvw+VEjIGhXcJzhZg@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, mpm-VDJrAJ4Gl5ZBDgjK7y7TUQ@public.gmane.org, alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org List-Id: linux-api@vger.kernel.org Andrew Morton a =E9crit : > On Mon, 2 Feb 2009 11:20:09 -0700 > Jonathan Corbet wrote: >=20 >> Matt Mackall suggested converting epoll's ep_lock to a bitlock as a = way of >> saving space in struct file. This patch makes that change. >=20 > hrm. bit_spin_lock() makes people upset (large penguiny people). ii= rc > it doesn't have all the correct/well-understood memory/compiler > ordering semantics which spinlocks have. And lockdep doesn't know ab= out > it. >=20 In a previous attempt (2005), I suggested using a single global lock. http://search.luky.org/linux-kernel.2005/msg50862.html Probably an array of hashed spinlocks would be more than enough. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755973AbZBCWQc (ORCPT ); Tue, 3 Feb 2009 17:16:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752203AbZBCWQW (ORCPT ); Tue, 3 Feb 2009 17:16:22 -0500 Received: from gw1.cosmosbay.com ([212.99.114.194]:48292 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751627AbZBCWQV convert rfc822-to-8bit (ORCPT ); Tue, 3 Feb 2009 17:16:21 -0500 X-Greylist: delayed 1198 seconds by postgrey-1.27 at vger.kernel.org; Tue, 03 Feb 2009 17:16:21 EST Message-ID: <4988BD4E.8080206@cosmosbay.com> Date: Tue, 03 Feb 2009 22:55:26 +0100 From: Eric Dumazet User-Agent: Thunderbird 2.0.0.19 (Windows/20081209) MIME-Version: 1.0 To: Andrew Morton CC: Jonathan Corbet , linux-kernel@vger.kernel.org, andi@firstfloor.org, oleg@redhat.com, viro@ZenIV.linux.org.uk, davidel@xmailserver.org, davem@davemloft.net, hch@lst.de, linux-api@vger.kernel.org, mpm@selenic.com, alan@lxorguk.ukuu.org.uk Subject: Re: [PATCH 2/4] Convert epoll to a bitlock References: <1233598811-6871-1-git-send-email-corbet@lwn.net> <1233598811-6871-3-git-send-email-corbet@lwn.net> <20090203133942.2ecec281.akpm@linux-foundation.org> In-Reply-To: <20090203133942.2ecec281.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-1.6 (gw1.cosmosbay.com [0.0.0.0]); Tue, 03 Feb 2009 22:55:26 +0100 (CET) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton a écrit : > On Mon, 2 Feb 2009 11:20:09 -0700 > Jonathan Corbet wrote: > >> Matt Mackall suggested converting epoll's ep_lock to a bitlock as a way of >> saving space in struct file. This patch makes that change. > > hrm. bit_spin_lock() makes people upset (large penguiny people). iirc > it doesn't have all the correct/well-understood memory/compiler > ordering semantics which spinlocks have. And lockdep doesn't know about > it. > In a previous attempt (2005), I suggested using a single global lock. http://search.luky.org/linux-kernel.2005/msg50862.html Probably an array of hashed spinlocks would be more than enough.