Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753680Ab2KTPSv (ORCPT ); Tue, 20 Nov 2012 10:18:51 -0500 Received: from mail-pb0-f46.google.com ([209.85.160.46]:45101 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753601Ab2KTPSs (ORCPT ); Tue, 20 Nov 2012 10:18:48 -0500 Message-ID: <50AB9F4A.5050500@gmail.com> Date: Tue, 20 Nov 2012 23:18:34 +0800 From: Jiang Liu User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121028 Thunderbird/16.0.2 MIME-Version: 1.0 To: Andrew Morton CC: Wen Congyang , David Rientjes , Jiang Liu , Maciej Rutecki , Chris Clayton , "Rafael J . Wysocki" , Mel Gorman , Minchan Kim , KAMEZAWA Hiroyuki , Michal Hocko , Jianguo Wu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFT PATCH v1 4/5] mm: provide more accurate estimation of pages occupied by memmap References: <20121115112454.e582a033.akpm@linux-foundation.org> <1353254850-27336-1-git-send-email-jiang.liu@huawei.com> <1353254850-27336-5-git-send-email-jiang.liu@huawei.com> <20121119154240.91efcc53.akpm@linux-foundation.org> In-Reply-To: <20121119154240.91efcc53.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1944 Lines: 54 On 11/20/2012 07:42 AM, Andrew Morton wrote: > On Mon, 19 Nov 2012 00:07:29 +0800 > Jiang Liu wrote: > >> If SPARSEMEM is enabled, it won't build page structures for >> non-existing pages (holes) within a zone, so provide a more accurate >> estimation of pages occupied by memmap if there are big holes within >> the zone. >> >> And pages for highmem zones' memmap will be allocated from lowmem, >> so charge nr_kernel_pages for that. >> >> ... >> >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -4435,6 +4435,22 @@ void __init set_pageblock_order(void) >> >> #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */ >> >> +static unsigned long calc_memmap_size(unsigned long spanned_pages, >> + unsigned long present_pages) >> +{ >> + unsigned long pages = spanned_pages; >> + >> + /* >> + * Provide a more accurate estimation if there are big holes within >> + * the zone and SPARSEMEM is in use. >> + */ >> + if (spanned_pages > present_pages + (present_pages >> 4) && >> + IS_ENABLED(CONFIG_SPARSEMEM)) >> + pages = present_pages; >> + >> + return PAGE_ALIGN(pages * sizeof(struct page)) >> PAGE_SHIFT; >> +} > > Please explain the ">> 4" heuristc more completely - preferably in both > the changelog and code comments. Why can't we calculate this > requirement exactly? That might require a second pass, but that's OK for > code like this? Hi Andrew, A normal x86 platform always have some holes within the DMA ZONE, so the ">> 4" heuristic is to avoid applying this adjustment to the DMA ZONE on x86 platforms. Because the memmap_size is just an estimation, I feel it's OK to remove the ">> 4" heuristic, that shouldn't affect much. Thanks Gerry -- 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/