From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id B5A196B0083 for ; Sun, 8 Nov 2009 07:52:08 -0500 (EST) Date: Sun, 8 Nov 2009 13:51:35 +0100 From: Ingo Molnar Subject: Re: [PATCH 02/11] Add "handle page fault" PV helper. Message-ID: <20091108125135.GA13099@elte.hu> References: <1257076590-29559-1-git-send-email-gleb@redhat.com> <1257076590-29559-3-git-send-email-gleb@redhat.com> <20091102092214.GB8933@elte.hu> <20091102160410.GF27911@redhat.com> <20091102161248.GB15423@elte.hu> <20091102162234.GH27911@redhat.com> <20091102162941.GC14544@elte.hu> <20091102174208.GJ27911@redhat.com> <20091108113654.GO11372@elte.hu> <4AF6BCE5.3030701@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AF6BCE5.3030701@redhat.com> Sender: owner-linux-mm@kvack.org To: Avi Kivity Cc: Gleb Natapov , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "H. Peter Anvin" , Thomas Gleixner , Fr??d??ric Weisbecker List-ID: * Avi Kivity wrote: > On 11/08/2009 01:36 PM, Ingo Molnar wrote: > >>Three existing callbacks are: kmemcheck, mmiotrace, notifier. Two > >>of them kmemcheck, mmiotrace are enabled only for debugging, should > >>not be performance concern. And notifier call sites (two of them) > >>are deliberately, as explained by comment, not at the function entry, > >>so can't be unified with others. (And kmemcheck also has two different > >>call site BTW) > > > > We want mmiotrace to be generic distro capable so the overhead when > > the hook is not used is of concern. > > Maybe we should generalize paravirt-ops patching in case if (x) f() is > deemed too expensive. Yes, that's a nice idea. We have quite a number of 'conditional callbacks' in various critical paths that could be made lighter via such a technique. It would also free new callbacks from the 'it increases overhead even if unused' criticism and made it easier to add them. Ingo -- 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