Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932477Ab0DGBru (ORCPT ); Tue, 6 Apr 2010 21:47:50 -0400 Received: from mail-gw0-f46.google.com ([74.125.83.46]:36214 "EHLO mail-gw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932438Ab0DGBrp convert rfc822-to-8bit (ORCPT ); Tue, 6 Apr 2010 21:47:45 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=f1bkx7Pv7vnaFW16WaEOzMaqyXr9f95F+FuIQorXh70A1LTpzNSeLlR9G6wXHAcyz9 USdJ02eM+bZQzC3LZ/lGUw0OU3+FDCdGety8OsYfBPa5llldYeqtK7ML+FlqsmMc8lob xx8H5zABofqVWXjnYtmub8Sky82Nir8+fjxIo= MIME-Version: 1.0 In-Reply-To: <4BBBC470.4050002@zytor.com> References: <4BBB7AC9.5060008@zytor.com> <4BBB8F07.60401@zytor.com> <3715922601579231267@unknownmsgid> <4BBBC470.4050002@zytor.com> Date: Tue, 6 Apr 2010 20:47:44 -0500 Message-ID: Subject: Re: why choose 896MB to the start point of ZONE_HIGHMEM From: Xianghua Xiao To: "H. Peter Anvin" Cc: Youngwhan Song , Venkatram Tummala , Joel Fernandes , Frank Hu , hayfeng Lee , "linux-kernel@vger.kernel.org" , "linux-kernel@zh-kernel.org" , "kernelnewbies@nl.linux.org" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1541 Lines: 38 If the last 128MB out of the kernel 1GB space is used to for highmen, meanwhile it's also used for IO/vmalloc, how does this work? Xianghua On Tue, Apr 6, 2010 at 6:32 PM, H. Peter Anvin wrote: > On 04/06/2010 04:27 PM, Youngwhan Song wrote: >> Nice explanation, Venkatram, >> >> Just one question pop up mind. >> >> What if actual physical memory is only 256MB? How does kernel divide >> virtual memory? Do we need to specify the region to kernel? Or will >> kernel itself decide it automatically? >> > > If there is less than 896 MB of physical memory, the vmalloc region is > automatically extended (in your case, it will be 768 MB in size.)  There > will be no HIGHMEM in such a case, and if you are compiling your own > kernel you will gain considerable speed by disabling HIGHMEM support > completely. > > This, of course, was the norm back when Linux was first created, and a > typical amount of memory was 8 MB or so.  That we'd have gigabytes of > memory seemed very distant at the time. > >        -hpa > -- > 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/ > -- 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/