Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759050Ab1D0Qg4 (ORCPT ); Wed, 27 Apr 2011 12:36:56 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:37484 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753280Ab1D0Qgz (ORCPT ); Wed, 27 Apr 2011 12:36:55 -0400 Subject: Re: [PATCH] convert parisc to sparsemem (was Re: [PATCH v3] mm: make expand_downwards symmetrical to expand_upwards) From: Dave Hansen To: James Bottomley Cc: Christoph Lameter , KOSAKI Motohiro , David Rientjes , Pekka Enberg , Michal Hocko , Andrew Morton , Hugh Dickins , linux-mm@kvack.org, LKML , linux-parisc@vger.kernel.org, Ingo Molnar , x86 maintainers , Tejun Heo , Mel Gorman , Andy Whitcroft In-Reply-To: <1303583657.4116.11.camel@mulgrave.site> References: <1303337718.2587.51.camel@mulgrave.site> <20110421221712.9184.A69D9226@jp.fujitsu.com> <1303403847.4025.11.camel@mulgrave.site> <1303411537.9048.3583.camel@nimitz> <1303507985.2590.47.camel@mulgrave.site> <1303583657.4116.11.camel@mulgrave.site> Content-Type: text/plain; charset="ISO-8859-1" Date: Wed, 27 Apr 2011 09:36:29 -0700 Message-ID: <1303922189.9516.33.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1943 Lines: 42 On Sat, 2011-04-23 at 13:34 -0500, James Bottomley wrote: > This is the preliminary conversion. It's very nasty on parisc because > the memory allocation isn't symmetric anymore: under DISCONTIGMEM, we > push all memory into bootmem and then let free_all_bootmem() do the > magic for us; Urg, that's unfortunate. I bet we could fairly easily teach the bootmem allocator to allow a couple of bootmem_data's to hang off of an individual pgdat. Put each pmem_ranges in one of those instead of a pgdat. That would at least help with the bitmap size explosion and extra loops. > now we have to do separate initialisations for ranges > because SPARSEMEM can't do multi-range boot memory. It's also got the > horrible hack that I only use the first found range for bootmem. I'm > not sure if this is correct (it won't be if the first found range can be > under about 50MB because we'll run out of bootmem during boot) ... we > might have to sort the ranges and use the larges, but that will involve > us in even more hackery around the bootmem reservations code. > > The boot sequence got a few seconds slower because now all of the loops > over our pfn ranges actually have to skip through the holes (which takes > time for 64GB). Which iterations were these, btw? All of the ones I saw the patch touch seemed to be running over just a single pmem_range. > All in all, I've not been very impressed with SPARSEMEM over > DISCONTIGMEM. It seems to have a lot of rough edges (necessitating > exception code) which DISCONTIGMEM just copes with. We definitely need to look at extending it to cover bootmem-time a bit. Is that even worth it these days with the no-bootmem bits around? -- Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/