From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [PATCHv4 27/39] x86-64, mm: proper alignment mappings with hugepages Date: Tue, 25 Jun 2013 09:46:24 -0700 Message-ID: <51C9C960.6070706@sr71.net> References: <1368321816-17719-1-git-send-email-kirill.shutemov@linux.intel.com> <1368321816-17719-28-git-send-email-kirill.shutemov@linux.intel.com> <519BFBA9.7040007@sr71.net> <20130625145655.68DCBE0090@blue.fi.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Andrea Arcangeli , Andrew Morton , Al Viro , Hugh Dickins , Wu Fengguang , Jan Kara , Mel Gorman , linux-mm@kvack.org, Andi Kleen , Matthew Wilcox , "Kirill A. Shutemov" , Hillf Danton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: "Kirill A. Shutemov" Return-path: In-Reply-To: <20130625145655.68DCBE0090@blue.fi.intel.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On 06/25/2013 07:56 AM, Kirill A. Shutemov wrote: > Dave Hansen wrote: >> On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote: >>> +static inline unsigned long mapping_align_mask(struct address_space *mapping) >>> +{ >>> + if (mapping_can_have_hugepages(mapping)) >>> + return PAGE_MASK & ~HPAGE_MASK; >>> + return get_align_mask(); >>> +} >> >> get_align_mask() appears to be a bit more complicated to me than just a >> plain old mask. Are you sure you don't need to pick up any of its >> behavior for the mapping_can_have_hugepages() case? > > get_align_mask() never returns more strict mask then we do in > mapping_can_have_hugepages() case. > > I can modify it this way: > > unsigned long mask = get_align_mask(); > > if (mapping_can_have_hugepages(mapping)) > mask &= PAGE_MASK & ~HPAGE_MASK; > return mask; > > But it looks more confusing for me. What do you think? Personally, I find that a *LOT* more clear. The &= pretty much spells out what you said in your explanation: get_align_mask()'s mask can only be made more strict when we encounter a huge page. The relationship between the two masks is not apparent at all in your original code. This is all nitpicking though, I just wanted to make sure you'd considered if you were accidentally changing behavior. -- 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751410Ab3FYQq1 (ORCPT ); Tue, 25 Jun 2013 12:46:27 -0400 Received: from www.sr71.net ([198.145.64.142]:42449 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751223Ab3FYQq0 (ORCPT ); Tue, 25 Jun 2013 12:46:26 -0400 Message-ID: <51C9C960.6070706@sr71.net> Date: Tue, 25 Jun 2013 09:46:24 -0700 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: "Kirill A. Shutemov" CC: Andrea Arcangeli , Andrew Morton , Al Viro , Hugh Dickins , Wu Fengguang , Jan Kara , Mel Gorman , linux-mm@kvack.org, Andi Kleen , Matthew Wilcox , "Kirill A. Shutemov" , Hillf Danton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv4 27/39] x86-64, mm: proper alignment mappings with hugepages References: <1368321816-17719-1-git-send-email-kirill.shutemov@linux.intel.com> <1368321816-17719-28-git-send-email-kirill.shutemov@linux.intel.com> <519BFBA9.7040007@sr71.net> <20130625145655.68DCBE0090@blue.fi.intel.com> In-Reply-To: <20130625145655.68DCBE0090@blue.fi.intel.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/25/2013 07:56 AM, Kirill A. Shutemov wrote: > Dave Hansen wrote: >> On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote: >>> +static inline unsigned long mapping_align_mask(struct address_space *mapping) >>> +{ >>> + if (mapping_can_have_hugepages(mapping)) >>> + return PAGE_MASK & ~HPAGE_MASK; >>> + return get_align_mask(); >>> +} >> >> get_align_mask() appears to be a bit more complicated to me than just a >> plain old mask. Are you sure you don't need to pick up any of its >> behavior for the mapping_can_have_hugepages() case? > > get_align_mask() never returns more strict mask then we do in > mapping_can_have_hugepages() case. > > I can modify it this way: > > unsigned long mask = get_align_mask(); > > if (mapping_can_have_hugepages(mapping)) > mask &= PAGE_MASK & ~HPAGE_MASK; > return mask; > > But it looks more confusing for me. What do you think? Personally, I find that a *LOT* more clear. The &= pretty much spells out what you said in your explanation: get_align_mask()'s mask can only be made more strict when we encounter a huge page. The relationship between the two masks is not apparent at all in your original code. This is all nitpicking though, I just wanted to make sure you'd considered if you were accidentally changing behavior.