From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx171.postini.com [74.125.245.171]) by kanga.kvack.org (Postfix) with SMTP id 7FFF16B006C for ; Tue, 15 Jan 2013 17:50:57 -0500 (EST) Received: from /spool/local by e32.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 15 Jan 2013 15:50:56 -0700 Received: from d03relay03.boulder.ibm.com (d03relay03.boulder.ibm.com [9.17.195.228]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 911401FF001C for ; Tue, 15 Jan 2013 15:50:43 -0700 (MST) Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by d03relay03.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r0FMosSq198666 for ; Tue, 15 Jan 2013 15:50:54 -0700 Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1]) by d03av03.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r0FMorMm000799 for ; Tue, 15 Jan 2013 15:50:54 -0700 Message-ID: <50F5DD45.4060603@linux.vnet.ibm.com> Date: Tue, 15 Jan 2013 14:50:45 -0800 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [RFCv3][PATCH 1/3] create slow_virt_to_phys() References: <20130109185904.DD641DCE@kernel.stglabs.ibm.com> <50F5B214.5060604@zytor.com> In-Reply-To: <50F5B214.5060604@zytor.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "H. Peter Anvin" Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Gleb Natapov , Avi Kivity , Ingo Molnar , x86@kernel.org, Marcelo Tosatti On 01/15/2013 11:46 AM, H. Peter Anvin wrote: > I object to this switch statement. If we are going to create new > primitives, let's create a primitive that embody this and put it in > pgtypes_types.h, especially since it is simply an algorithmic operation: Yeah, that's a good point. I did at least copy part of the switch from elsewhere in the file, so there's certainly room for consolidating some things. > static inline unsigned long page_level_size(int level) > { > return (PAGE_SIZE/PGDIR_SIZE) << (PGDIR_SHIFT*level); > } > static inline unsigned long page_level_shift(int level) > { > return (PAGE_SHIFT-PGDIR_SHIFT) + (PGDIR_SHIFT*level); > } (PAGE_SHIFT-PGDIR_SHIFT) == -27, so this can't possibly work, right? How about something like this? /* * Note: this only holds true for pagetable levels where PTEs can be * present. It would break if you used it on the PGD level where PAE * is in use. It basically assumes that the shift between _all_ * adjacent levels of the pagetables are the same as the lowest-level * shift. */ #define PG_SHIFT_PER_LEVEL (PMD_SHIFT-PAGE_SHIFT) static inline unsigned long page_level_shift(int level) { return PAGE_SHIFT + (level - PG_LEVEL_4K) * PG_SHIFT_PER_LEVEL; } static inline unsigned long page_level_size(int level) { return 1 << page_level_shift(level); } The generated code for page_level_size() looks pretty good, despite it depending on page_level_shift(), so we might as well leave it defined this way for simplicity: 0000000000400610 : 400610: 8d 7c bf fb lea -0x5(%rdi,%rdi,4),%edi 400614: b8 01 00 00 00 mov $0x1,%eax 400619: 8d 4c 3f 0c lea 0xc(%rdi,%rdi,1),%ecx 40061d: d3 e0 shl %cl,%eax 40061f: c3 retq I'll send out another series doing this. -- 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