From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756796Ab1KQRVR (ORCPT ); Thu, 17 Nov 2011 12:21:17 -0500 Received: from mail-yx0-f174.google.com ([209.85.213.174]:54578 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753822Ab1KQRVQ (ORCPT ); Thu, 17 Nov 2011 12:21:16 -0500 Message-ID: <4EC5428A.6030700@gmail.com> Date: Thu, 17 Nov 2011 09:21:14 -0800 From: David Daney User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 MIME-Version: 1.0 To: David Rientjes CC: "ralf@linux-mips.org" , "linux-mips@linux-mips.org" , Andrew Morton , "linux-kernel@vger.kernel.org" , David Daney Subject: Re: [PATCH] hugetlb: Provide a default HPAGE_SHIFT if !CONFIG_HUGETLB_PAGE References: <1321472611-13283-1-git-send-email-ddaney.cavm@gmail.com> <4EC43488.3070400@gmail.com> <4EC44AD0.5070800@gmail.com> <4EC45CAE.1000704@gmail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/16/2011 08:56 PM, David Rientjes wrote: > On Wed, 16 Nov 2011, David Daney wrote: > >>>> It is a well established kernel idiom to supply dummy values for symbols >>>> that >>>> are required to be defined in order to form a syntactically correct C >>>> program, >>>> but that are known by the programmer to be used only on dead code paths. >>>> >>>> This is exactly what we are doing here. >>>> >>>> To do otherwise requires that code be cluttered with #ifdefery. >>>> >>> >>> You're wrong, >> >> Ok, then please tell me why: >> >> 1) the dummy version of is_vm_hugetlb_page() exists in hugetlb_inline.h? >> 2) the dummy version of PageHuge() exists in hugetlb.h [...] > > To avoid the #ifdef's, Good, now we are on the same page. The answer is not, as first suggested, to sprinkle #ifdefs all over the place, but ... > but you'll notice that they return either NULL, 0, > or are a no-op. We don't substitute real values in dummy functions where > they could be used in generic code as though they were valid. That's the > problem with defining HPAGE_SHIFT to be PAGE_SHIFT and, yes, defining > HPAGE_MASK and HPAGE_SIZE as well shouldn't be done and should be removed. > > We expect HPAGE_* to represent hugepages, not the native page size of the > bare metal. This is why we do things like > > #define HPAGE_PMD_SHIFT ({ BUG(); 0; }) > #define HPAGE_PMD_MASK ({ BUG(); 0; }) > #define HPAGE_PMD_SIZE ({ BUG(); 0; }) ... rather to fix HPAGE_SHIFT, HPAGE_MASK, and HPAGE_SIZE to be more like these. I will generate a version of the patch that does this, noting that it the addition of a dummy definition of HPAGE_SHIFT is added to facilitate cleaner architecture specific code for MIPS patches in linux-next. Thanks, David Daney > > for CONFIG_TRANSPARENT_HUGEPAGE=n. We don't want to pretend that they're > valid outside the context of hugepages. > > We also never use HPAGE_SHIFT, HPAGE_MASK, or HPAGE_SIZE in generic code > that isn't dependent on CONFIG_HUGETLB_PAGE. If you'd like to submit a > patch to fix this in the mips tree, then that would be good, and if you'd > like to submit a patch to remove these dummy definitions all together by > auditing other arch code, then that would be great. >