From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [patch 1/2]: x86: implement pte_special Date: Thu, 27 Mar 2008 20:44:31 -0700 (PDT) Message-ID: <20080327.204431.201380891.davem@davemloft.net> References: <20080328025541.GB8083@wotan.suse.de> <20080327.202334.250213398.davem@davemloft.net> <20080328033149.GD8083@wotan.suse.de> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080328033149.GD8083-B4tOwbsTzaBolqkO4TVVkw@public.gmane.org> Sender: linux-arch-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: To: npiggin-l3A5Bk7waGM@public.gmane.org Cc: akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, shaggy-V7BBcbaFuwjMbYB6QlFGEg@public.gmane.org, axboe-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org From: Nick Piggin Date: Fri, 28 Mar 2008 04:31:50 +0100 > Basically, the pfn-based mapping insertion (vm_insert_pfn, remap_pfn_range) > calls pte_mkspecial. And that tells fast_gup "hands off". I don't think it's wise to allocate a "soft PTE bit" for this on every platform, especially for such a limited use case. Is it feasible to test the page instead? Or are we talking about cases where there may not be a backing page? If the issue is to discern things like I/O mappings and such vs. real pages, there are ways a platform can handle that without a special bit. That would leave us with real memory that does not have backing page structs, and we have a way to test that too. The special PTE bit seems superfluous to me. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:48057 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753237AbYC1Dob (ORCPT ); Thu, 27 Mar 2008 23:44:31 -0400 Date: Thu, 27 Mar 2008 20:44:31 -0700 (PDT) Message-ID: <20080327.204431.201380891.davem@davemloft.net> Subject: Re: [patch 1/2]: x86: implement pte_special From: David Miller In-Reply-To: <20080328033149.GD8083@wotan.suse.de> References: <20080328025541.GB8083@wotan.suse.de> <20080327.202334.250213398.davem@davemloft.net> <20080328033149.GD8083@wotan.suse.de> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: npiggin@suse.de Cc: akpm@linux-foundation.org, shaggy@austin.ibm.com, axboe@oracle.com, linux-mm@kvack.org, linux-arch@vger.kernel.org, torvalds@linux-foundation.org Message-ID: <20080328034431.Llb8NBJysOQCqArTD_3d6YvOuUamcUCoI6OpfEMkrek@z> From: Nick Piggin Date: Fri, 28 Mar 2008 04:31:50 +0100 > Basically, the pfn-based mapping insertion (vm_insert_pfn, remap_pfn_range) > calls pte_mkspecial. And that tells fast_gup "hands off". I don't think it's wise to allocate a "soft PTE bit" for this on every platform, especially for such a limited use case. Is it feasible to test the page instead? Or are we talking about cases where there may not be a backing page? If the issue is to discern things like I/O mappings and such vs. real pages, there are ways a platform can handle that without a special bit. That would leave us with real memory that does not have backing page structs, and we have a way to test that too. The special PTE bit seems superfluous to me.