From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by kanga.kvack.org (Postfix) with ESMTP id DD41A6B007E for ; Fri, 4 Mar 2016 09:11:55 -0500 (EST) Received: by mail-wm0-f53.google.com with SMTP id p65so30886722wmp.0 for ; Fri, 04 Mar 2016 06:11:55 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id ld8si4199069wjc.77.2016.03.04.06.11.54 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 04 Mar 2016 06:11:54 -0800 (PST) Subject: Re: [PATCH v2] mm: exclude ZONE_DEVICE from GFP_ZONE_TABLE References: <20160302002829.38211.89593.stgit@dwillia2-desk3.amr.corp.intel.com> From: Vlastimil Babka Message-ID: <56D997A6.7070200@suse.cz> Date: Fri, 4 Mar 2016 15:11:50 +0100 MIME-Version: 1.0 In-Reply-To: <20160302002829.38211.89593.stgit@dwillia2-desk3.amr.corp.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams , akpm@linux-foundation.org Cc: Rik van Riel , Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mel Gorman , Mark , Joonsoo Kim , Sudip Mukherjee On 03/02/2016 01:32 AM, Dan Williams wrote: > ZONE_DEVICE (merged in 4.3) and ZONE_CMA (proposed) are examples of new > mm zones that are bumping up against the current maximum limit of 4 > zones, i.e. 2 bits in page->flags for the GFP_ZONE_TABLE. > > The GFP_ZONE_TABLE poses an interesting constraint since > include/linux/gfp.h gets included by the 32-bit portion of a 64-bit > build. We need to be careful to only build the table for zones that > have a corresponding gfp_t flag. GFP_ZONES_SHIFT is introduced for this > purpose. This patch does not attempt to solve the problem of adding a > new zone that also has a corresponding GFP_ flag. > > Vlastimil points out that ZONE_DEVICE, by depending on x86_64 and > SPARSEMEM_VMEMMAP implies that SECTIONS_WIDTH is zero. In other words ^ by default Because CONFIG_SPARSEMEM_VMEMMAP can still be disabled by the user. > even though ZONE_DEVICE does not fit in GFP_ZONE_TABLE it is free to > consume another bit in page->flags (expand ZONES_WIDTH) with room to > spare. So it's still possible to configure the x86_64 kernel such that you get "#warning Unfortunate NUMA and NUMA Balancing config". But it requires some effort to override the defaults, and it's not breaking build or runtime. BTW I was able to get that warning even with your previous patch that limited NODES_WIDTH, so that wasn't a solution for this anyway. This patch is simpler and better. > Link: https://bugzilla.kernel.org/show_bug.cgi?id=110931 > Fixes: 033fbae988fc ("mm: ZONE_DEVICE for "device memory"") > Cc: Mel Gorman > Cc: Rik van Riel > Cc: Joonsoo Kim > Cc: Dave Hansen > Cc: Sudip Mukherjee > Reported-by: Mark > Reported-by: Vlastimil Babka > Signed-off-by: Dan Williams Acked-by: Vlastimil Babka -- 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