From mboxrd@z Thu Jan 1 00:00:00 1970 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: owner-linux-mm@kvack.org From: Nick Piggin Date: Fri, 28 Mar 2008 04:31:50 +0100 Return-Path: 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 List-ID: > 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. -- 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