From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754551AbZFCUyM (ORCPT ); Wed, 3 Jun 2009 16:54:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753530AbZFCUx5 (ORCPT ); Wed, 3 Jun 2009 16:53:57 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:54649 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753507AbZFCUxz (ORCPT ); Wed, 3 Jun 2009 16:53:55 -0400 To: Davide Libenzi Cc: Al Viro , Linux Kernel Mailing List , linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Hugh Dickins , Tejun Heo , Alexey Dobriyan , Linus Torvalds , Alan Cox , Greg Kroah-Hartman , Nick Piggin , Andrew Morton , Christoph Hellwig , "Eric W. Biederman" Subject: Re: [PATCH 18/23] vfs: Teach epoll to use file_hotplug_lock References: <1243893048-17031-18-git-send-email-ebiederm@xmission.com> From: ebiederm@xmission.com (Eric W. Biederman) Date: Wed, 03 Jun 2009 13:53:48 -0700 In-Reply-To: (Davide Libenzi's message of "Wed\, 3 Jun 2009 07\:57\:40 -0700 \(PDT\)") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in02.mta.xmission.com;;;ip=76.21.114.89;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 76.21.114.89 X-SA-Exim-Rcpt-To: davidel@xmailserver.org, ebiederm@aristanetworks.com, hch@infradead.org, akpm@linux-foundation.org, npiggin@suse.de, gregkh@suse.de, alan@lxorguk.ukuu.org.uk, torvalds@linux-foundation.org, adobriyan@gmail.com, tj@kernel.org, hugh@veritas.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, viro@ZenIV.linux.org.uk X-SA-Exim-Mail-From: ebiederm@xmission.com X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: No (on in02.mta.xmission.com); Unknown failure Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Davide Libenzi writes: > On Tue, 2 Jun 2009, Eric W. Biederman wrote: > >> I am not clear what problem you have. >> >> Is it the sprinkling the code that takes and removes the lock? Just >> the VFS needs to be involved with that. It is a slightly larger >> surface area than doing the work inside the file operations as we >> sometimes call the same method from 3-4 different places but it is >> definitely a bounded problem. >> >> Is it putting in the handful lines per subsystem to actually use this >> functionality? At that level something generic that is maintained >> outside of the subsystem is better than the mess we have with 4-5 >> different implementations in the subsystems that need it, each having >> a different assortment of bugs. > > Come on, only in the open fast path, there are at least two spin > lock/unlock and two atomic ops. Without even starting to count all the > extra branches and software added. > Is this stuff *really* needed, or we can faitly happily live w/out? ???? What code are you talking about? To the open path a few memory writes and a smp_wmb. No atomics and no spin lock/unlocks. Are you complaining because I retain the file_list? Eric From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id D59346B004D for ; Wed, 3 Jun 2009 16:53:58 -0400 (EDT) Subject: Re: [PATCH 18/23] vfs: Teach epoll to use file_hotplug_lock References: <1243893048-17031-18-git-send-email-ebiederm@xmission.com> From: ebiederm@xmission.com (Eric W. Biederman) Date: Wed, 03 Jun 2009 13:53:48 -0700 In-Reply-To: (Davide Libenzi's message of "Wed\, 3 Jun 2009 07\:57\:40 -0700 \(PDT\)") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org To: Davide Libenzi Cc: Al Viro , Linux Kernel Mailing List , linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Hugh Dickins , Tejun Heo , Alexey Dobriyan , Linus Torvalds , Alan Cox , Greg Kroah-Hartman , Nick Piggin , Andrew Morton , Christoph Hellwig , "Eric W. Biederman" List-ID: Davide Libenzi writes: > On Tue, 2 Jun 2009, Eric W. Biederman wrote: > >> I am not clear what problem you have. >> >> Is it the sprinkling the code that takes and removes the lock? Just >> the VFS needs to be involved with that. It is a slightly larger >> surface area than doing the work inside the file operations as we >> sometimes call the same method from 3-4 different places but it is >> definitely a bounded problem. >> >> Is it putting in the handful lines per subsystem to actually use this >> functionality? At that level something generic that is maintained >> outside of the subsystem is better than the mess we have with 4-5 >> different implementations in the subsystems that need it, each having >> a different assortment of bugs. > > Come on, only in the open fast path, there are at least two spin > lock/unlock and two atomic ops. Without even starting to count all the > extra branches and software added. > Is this stuff *really* needed, or we can faitly happily live w/out? ???? What code are you talking about? To the open path a few memory writes and a smp_wmb. No atomics and no spin lock/unlocks. Are you complaining because I retain the file_list? Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org