From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f177.google.com (mail-yk0-f177.google.com [209.85.160.177]) by kanga.kvack.org (Postfix) with ESMTP id 60E176B0005 for ; Tue, 26 Jan 2016 20:37:39 -0500 (EST) Received: by mail-yk0-f177.google.com with SMTP id a85so223733879ykb.1 for ; Tue, 26 Jan 2016 17:37:39 -0800 (PST) Received: from mail-yk0-x235.google.com (mail-yk0-x235.google.com. [2607:f8b0:4002:c07::235]) by mx.google.com with ESMTPS id w201si1380707ywg.348.2016.01.26.17.37.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Jan 2016 17:37:38 -0800 (PST) Received: by mail-yk0-x235.google.com with SMTP id a85so223733538ykb.1 for ; Tue, 26 Jan 2016 17:37:38 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20160127011817.GA7398@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> Date: Tue, 26 Jan 2016 17:37:38 -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 5:18 PM, Joonsoo Kim wrote: > Hello, > > On Tue, Jan 26, 2016 at 03:11:36PM -0800, Dan Williams wrote: >> On Tue, Jan 26, 2016 at 2:51 PM, Andrew Morton >> wrote: >> > On Tue, 26 Jan 2016 14:33:48 -0800 Dan Williams wrote: >> > >> >> >> 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? >> >> >> >> Last I tried I hit this warning in mm/memory.c >> >> >> >> #warning Unfortunate NUMA and NUMA Balancing config, growing >> >> page-frame for last_cpupid. >> > >> > Well yes, it may take a bit of work - perhaps salvaging a bit from >> > somewhere else if poss. But that might provide a better overall >> > solution so could you please have a think? >> > >> >> Will do, especially since other efforts are feeling the pinch on the >> MAX_NR_ZONES limitation. > > 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. -- 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