From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f177.google.com (mail-ob0-f177.google.com [209.85.214.177]) by kanga.kvack.org (Postfix) with ESMTP id 2DCFA6B0005 for ; Fri, 11 Mar 2016 16:40:21 -0500 (EST) Received: by mail-ob0-f177.google.com with SMTP id m7so125932913obh.3 for ; Fri, 11 Mar 2016 13:40:21 -0800 (PST) Received: from mail-ob0-x229.google.com (mail-ob0-x229.google.com. [2607:f8b0:4003:c01::229]) by mx.google.com with ESMTPS id b2si7956910oem.44.2016.03.11.13.40.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 11 Mar 2016 13:40:20 -0800 (PST) Received: by mail-ob0-x229.google.com with SMTP id fz5so126359950obc.0 for ; Fri, 11 Mar 2016 13:40:20 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1457730784-9890-2-git-send-email-matthew.r.wilcox@intel.com> References: <1457730784-9890-1-git-send-email-matthew.r.wilcox@intel.com> <1457730784-9890-2-git-send-email-matthew.r.wilcox@intel.com> Date: Fri, 11 Mar 2016 13:40:20 -0800 Message-ID: Subject: Re: [PATCH 1/3] pfn_t: Change the encoding From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: "linux-nvdimm@lists.01.org" , "linux-kernel@vger.kernel.org" , Linux MM , Matthew Wilcox , Dave Hansen On Fri, Mar 11, 2016 at 1:13 PM, Matthew Wilcox wrote: > By moving the flag bits to the bottom, we encourage commonality > between SGs with pages and those using pfn_t. We can also then insert > a pfn_t into a radix tree, as it uses the same two bits for indirect & > exceptional indicators. It's not immediately clear to me what we gain with SG entry commonality. The down side is that we lose the property that pfn_to_pfn_t() is a nop. This was Dave's suggestion so that the nominal case did not change the binary layout of a typical pfn. Can we just bit swizzle a pfn_t on insertion/retrieval from the radix? -- 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