From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f44.google.com (mail-pa0-f44.google.com [209.85.220.44]) by kanga.kvack.org (Postfix) with ESMTP id 90E4F6B0005 for ; Tue, 26 Jan 2016 22:52:16 -0500 (EST) Received: by mail-pa0-f44.google.com with SMTP id uo6so110915813pac.1 for ; Tue, 26 Jan 2016 19:52:16 -0800 (PST) Received: from lgeamrelo11.lge.com (LGEAMRELO11.lge.com. [156.147.23.51]) by mx.google.com with ESMTPS id g14si6361145pfd.189.2016.01.26.19.52.14 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 26 Jan 2016 19:52:15 -0800 (PST) Date: Wed, 27 Jan 2016 12:52:15 +0900 From: Joonsoo Kim Subject: Re: [RFC PATCH] mm: support CONFIG_ZONE_DEVICE + CONFIG_ZONE_DMA Message-ID: <20160127035215.GA7813@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams 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 07:23:59PM -0800, Dan Williams wrote: > 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. Yes, but, my point is that if someone need another zone like as ZONE_CMA, they couldn't get the benefit from this change. They need to re-investigate what bits they can reduce and need to re-do all things. If it is implemented more generally at this time, it can relieve their burden and less churn the code. It would be helpful for maintainability. Thanks. -- 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