From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f182.google.com (mail-yk0-f182.google.com [209.85.160.182]) by kanga.kvack.org (Postfix) with ESMTP id C817B6B0005 for ; Tue, 26 Jan 2016 16:48:15 -0500 (EST) Received: by mail-yk0-f182.google.com with SMTP id u68so88961925ykd.2 for ; Tue, 26 Jan 2016 13:48:15 -0800 (PST) Received: from mail-yk0-x22d.google.com (mail-yk0-x22d.google.com. [2607:f8b0:4002:c07::22d]) by mx.google.com with ESMTPS id i63si1138554ywe.375.2016.01.26.13.48.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Jan 2016 13:48:15 -0800 (PST) Received: by mail-yk0-x22d.google.com with SMTP id u68so88961619ykd.2 for ; Tue, 26 Jan 2016 13:48:15 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <56A7E846.30607@suse.cz> References: <20160126000639.358.89668.stgit@dwillia2-desk3.amr.corp.intel.com> <56A7E846.30607@suse.cz> Date: Tue, 26 Jan 2016 13:48:14 -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: Vlastimil Babka Cc: Andrew Morton , Rik van Riel , "linux-nvdimm@lists.01.org" , Dave Hansen , "linux-kernel@vger.kernel.org" , Christoph Hellwig , Linux MM , Ingo Molnar , Mel Gorman , "H. Peter Anvin" , Jerome Glisse , Sudip Mukherjee , Joonsoo Kim , Laura Abbott On Tue, Jan 26, 2016 at 1:42 PM, Vlastimil Babka wrote: > On 26.1.2016 1:06, 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. We want a single >> kernel image to be able to support legacy devices as well as next >> generation persistent memory platforms. >> >> 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. > > [+CC Joonsoo, Laura] > > Sounds like quite a hack :( Indeed... > Would it be possible to extend the bits encoding > zone? Potentially, ZONE_CMA could be added one day... Not without impacting the ability to quickly lookup the numa node and parent section for a page. See ZONES_WIDTH, NODES_WIDTH, and SECTIONS_WIDTH. My initial implementation of ZONE_DEVICE ran into this conflict when ZONES_SHIFT is > 2, and I fell back to cannibalizing ZONE_DMA. -- 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