From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f175.google.com (mail-yk0-f175.google.com [209.85.160.175]) by kanga.kvack.org (Postfix) with ESMTP id 95C056B0005 for ; Tue, 26 Jan 2016 22:24:00 -0500 (EST) Received: by mail-yk0-f175.google.com with SMTP id v14so226161633ykd.3 for ; Tue, 26 Jan 2016 19:24:00 -0800 (PST) Received: from mail-yk0-x22a.google.com (mail-yk0-x22a.google.com. [2607:f8b0:4002:c07::22a]) by mx.google.com with ESMTPS id 206si1508742ybu.139.2016.01.26.19.23.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Jan 2016 19:23:59 -0800 (PST) Received: by mail-yk0-x22a.google.com with SMTP id a85so226150397ykb.1 for ; Tue, 26 Jan 2016 19:23:59 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20160127021515.GA7562@js1304-P5Q-DELUXE> References: <20160126000639.358.89668.stgit@dwillia2-desk3.amr.corp.intel.com> <20160126141152.e1043d14502dcca17813afb3@linux-foundation.org> <20160126145153.44e4f38b04200209d133c0a3@linux-foundation.org> <20160127011817.GA7398@js1304-P5Q-DELUXE> <20160127021515.GA7562@js1304-P5Q-DELUXE> Date: Tue, 26 Jan 2016 19:23:59 -0800 Message-ID: Subject: Re: [RFC PATCH] mm: support CONFIG_ZONE_DEVICE + CONFIG_ZONE_DMA From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Andrew Morton , Rik van Riel , linux-nvdimm , Dave Hansen , "linux-kernel@vger.kernel.org" , Christoph Hellwig , Linux MM , Ingo Molnar , Mel Gorman , "H. Peter Anvin" , Jerome Glisse , Sudip Mukherjee On Tue, Jan 26, 2016 at 6:15 PM, Joonsoo Kim wrote: > On Tue, Jan 26, 2016 at 05:37:38PM -0800, Dan Williams wrote: >> On Tue, Jan 26, 2016 at 5:18 PM, Joonsoo Kim wrote: [..] >> > Please refer my previous attempt to add a new zone, ZONE_CMA. >> > >> > https://lkml.org/lkml/2015/2/12/84 >> > >> > It salvages a bit from SECTION_WIDTH by increasing section size. >> > Similarly, I guess we can reduce NODE_WIDTH if needed although >> > it could cause to reduce maximum node size. >> >> Dave pointed out to me that LAST__PID_SHIFT might be a better >> candidate to reduce to 7 bits. That field is for storing pids which >> are already bigger than 8 bits. If it is relying on the fact that >> pids don't rollover very often then likely the impact of 7-bits >> instead of 8 will be minimal. > > Hmm... I'm not sure it's possible or not, but, it looks not a general > solution. It will solve your problem because you are using 64 bit arch > but other 32 bit archs can't get the benefit. This is where the ZONE_CMA and ZONE_DEVICE efforts diverge. ZONE_DEVICE is meant to enable DMA access to hundreds of gigagbytes of persistent memory. A 64-bit-only limitation for ZONE_DEVICE is reasonable. -- 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