From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f178.google.com (mail-pf0-f178.google.com [209.85.192.178]) by kanga.kvack.org (Postfix) with ESMTP id 4FF036B0005 for ; Tue, 26 Jan 2016 17:11:54 -0500 (EST) Received: by mail-pf0-f178.google.com with SMTP id x125so163392pfb.0 for ; Tue, 26 Jan 2016 14:11:54 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id r6si4453777pap.212.2016.01.26.14.11.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Jan 2016 14:11:53 -0800 (PST) Date: Tue, 26 Jan 2016 14:11:52 -0800 From: Andrew Morton Subject: Re: [RFC PATCH] mm: support CONFIG_ZONE_DEVICE + CONFIG_ZONE_DMA Message-Id: <20160126141152.e1043d14502dcca17813afb3@linux-foundation.org> In-Reply-To: <20160126000639.358.89668.stgit@dwillia2-desk3.amr.corp.intel.com> References: <20160126000639.358.89668.stgit@dwillia2-desk3.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: Rik van Riel , linux-nvdimm@ml01.01.org, Dave Hansen , linux-kernel@vger.kernel.org, Christoph Hellwig , linux-mm@kvack.org, Ingo Molnar , Mel Gorman , "H. Peter Anvin" , Jerome Glisse , Sudip Mukherjee On Mon, 25 Jan 2016 16:06:40 -0800 Dan Williams wrote: > It appears devices requiring ZONE_DMA are still prevalent (see link > below). For this reason the proposal to require turning off ZONE_DMA to > enable ZONE_DEVICE is untenable in the short term. More than "short term". When can we ever nuke ZONE_DMA? This was a pretty big goof - the removal of ZONE_DMA whizzed straight past my attention, alas. In fact I never noticed the patch at all until I got some conflicts in -next a few weeks later (wasn't cc'ed). And then I didn't read the changelog closely enough. > We want a single > kernel image to be able to support legacy devices as well as next > generation persistent memory platforms. yup. > Towards this end, alias ZONE_DMA and ZONE_DEVICE to work around needing > to maintain a unique zone number for ZONE_DEVICE. Record the geometry > of ZONE_DMA at init (->init_spanned_pages) and use that information in > is_zone_device_page() to differentiate pages allocated via > devm_memremap_pages() vs true ZONE_DMA pages. Otherwise, use the > simpler definition of is_zone_device_page() when ZONE_DMA is turned off. > > Note that this also teaches the memory hot remove path that the zone may > not have sections for all pfn spans (->zone_dyn_start_pfn). > > A user visible implication of this change is potentially an unexpectedly > high "spanned" value in /proc/zoneinfo for the DMA zone. Well, all these icky tricks are to avoid increasing ZONES_SHIFT, yes? Is it possible to just use ZONES_SHIFT=3? Also, this "dynamically added pfn of the zone" thing is a new concept and I think it should be more completely documented somewhere in the code. -- 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