From mboxrd@z Thu Jan 1 00:00:00 1970 From: KOSAKI Motohiro Subject: Re: Arch specific mmap attributes (Was: mprotect pgprot handling weirdness) Date: Wed, 7 Apr 2010 15:03:45 +0900 (JST) Message-ID: <20100407095145.FB70.A69D9226@jp.fujitsu.com> References: <20100406185246.7E63.A69D9226@jp.fujitsu.com> <1270592111.13812.88.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:36254 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752922Ab0DGGDy (ORCPT ); Wed, 7 Apr 2010 02:03:54 -0400 In-Reply-To: <1270592111.13812.88.camel@pasglop> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Benjamin Herrenschmidt Cc: kosaki.motohiro@jp.fujitsu.com, linux-mm@kvack.org, "linux-kernel@vger.kernel.org" , linux-arch@vger.kernel.org > On Tue, 2010-04-06 at 19:26 +0900, KOSAKI Motohiro wrote: > > > Ok, I see. No biggie. The main deal remains how we want to do that > > > inside the kernel :-) I think the less horrible options here are > > > to either extend vm_flags to always be 64-bit, or add a separate > > > vm_map_attributes flag, and add the necessary bits and pieces to > > > prevent merge accross different attribute vma's. > > > > vma->vm_flags already have VM_SAO. Why do we need more flags? > > At least, I dislike to add separate flags member into vma. > > It might introduce unnecessary messy into vma merge thing. > > Well, we did shove SAO in there, and used up the very last vm_flag for > it a while back. Now I need another one, for little endian mappings. So > I'm stuck. > > But the problem goes further I believe. Archs do nowadays have quite an > interesting set of MMU attributes that it would be useful to expose to > some extent. Generally speaking, It seems no good idea. desktop and server world don't interest arch specific mmu attribute crap. because many many opensource and ISV library don't care it. I know highend hpc and embedded have differenct eco-system. they might want to use such strange mmu feature. I recommend to you are focusing popwerpc eco-system. I'm not against changing kernel internal. I only disagree mmu attribute fashion will be become used widely. > > Some powerpc's also provide storage keys for example and I think ARM > have something along those lines. There's interesting cachability > attributes too, on x86 as well. Being able to use such attributes to > request for example a relaxed ordering mapping on x86 might be useful. > > I think it basically boils down to either extend vm_flags to always be > 64-bit, which seems to be Nick preferred approach, or introduct a > vm_attributes with all the necessary changes to the merge code to take > it into account (not -that- hard tho, there's only half a page of > results in grep for these things :-)