Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761189AbYFFQ0T (ORCPT ); Fri, 6 Jun 2008 12:26:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754896AbYFFQ0J (ORCPT ); Fri, 6 Jun 2008 12:26:09 -0400 Received: from mx1.suse.de ([195.135.220.2]:48630 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751874AbYFFQ0I (ORCPT ); Fri, 6 Jun 2008 12:26:08 -0400 Date: Fri, 6 Jun 2008 18:26:03 +0200 From: Nick Piggin To: Peter Zijlstra Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org, paulus@samba.org, Paul E McKenney Subject: Re: [patch 3/7] mm: speculative page references Message-ID: <20080606162603.GB23939@wotan.suse.de> References: <20080605094300.295184000@nick.local0.net> <20080605094825.699347000@nick.local0.net> <1212762004.23439.119.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1212762004.23439.119.camel@twins> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1804 Lines: 48 On Fri, Jun 06, 2008 at 04:20:04PM +0200, Peter Zijlstra wrote: > On Thu, 2008-06-05 at 19:43 +1000, npiggin@suse.de wrote: > > plain text document attachment (mm-speculative-get_page-hugh.patch) > > > +static inline int page_cache_get_speculative(struct page *page) > > +{ > > + VM_BUG_ON(in_interrupt()); > > + > > +#ifndef CONFIG_SMP > > +# ifdef CONFIG_PREEMPT > > + VM_BUG_ON(!in_atomic()); > > +# endif > > + /* > > + * Preempt must be disabled here - we rely on rcu_read_lock doing > > + * this for us. > > Preemptible RCU is already in the tree, so I guess you'll have to > explcitly disable preemption if you require it. Oh, of course, I forget about preempt RCU, lucky for the comment. Good spotting. -- As per the comment here, we can only use that shortcut if rcu_read_lock disabled preemption. It would be somewhat annoying to have to put preempt_disable/preempt_enable around all callers in order to support this, but preempt RCU isn't going to be hugely performance critical anyway (and actually it actively trades performance for fewer preempt off sections), so it can use the slightly slower path quite happily. Index: linux-2.6/include/linux/pagemap.h =================================================================== --- linux-2.6.orig/include/linux/pagemap.h +++ linux-2.6/include/linux/pagemap.h @@ -111,7 +111,7 @@ static inline int page_cache_get_specula { VM_BUG_ON(in_interrupt()); -#ifndef CONFIG_SMP +#if !defined(CONFIG_SMP) && defined(CONFIG_CLASSIC_RCU) # ifdef CONFIG_PREEMPT VM_BUG_ON(!in_atomic()); # endif -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/