Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932789Ab3CRVRM (ORCPT ); Mon, 18 Mar 2013 17:17:12 -0400 Received: from terminus.zytor.com ([198.137.202.10]:39551 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756515Ab3CRVQy (ORCPT ); Mon, 18 Mar 2013 17:16:54 -0400 Message-ID: <514783B4.2030401@zytor.com> Date: Mon, 18 Mar 2013 14:14:28 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 MIME-Version: 1.0 To: Vivek Goyal CC: Yinghai Lu , "Eric W. Biederman" , Konrad Rzeszutek Wilk , Thomas Gleixner , Ingo Molnar , WANG Chao , linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86, kdump: Set crashkernel_low automatically References: <513E28B8.3000502@zytor.com> <20130311191031.GD12107@redhat.com> <20130311193824.GA14738@redhat.com> <20130318144603.GA20743@redhat.com> <20130318153348.GA25806@redhat.com> <514766B7.4070303@zytor.com> <20130318200048.GJ20743@redhat.com> In-Reply-To: <20130318200048.GJ20743@redhat.com> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1577 Lines: 41 On 03/18/2013 01:00 PM, Vivek Goyal wrote: > On Mon, Mar 18, 2013 at 12:10:47PM -0700, H. Peter Anvin wrote: >> On 03/18/2013 08:33 AM, Vivek Goyal wrote: >>> >>> Thinking more about it, if ongoing DMA is an issue, then setting up >>> software iotlb in those areas is also prone to being overwritten by >>> those DMAs. Hence, reserving memory low where no DMA is setup by first >>> kernel, seems somewhat safer. >>> >> >> Agreed. We really should reserve some memory low. > > So which approach do you like for reserving some memory low. > > - User specifies crashkernel_low=X to reserve some memory. Biggest problem > here is how does user know how much memory is required for setting up > swiotlb. > > - Take yinghai's patch where by default low memory for swiotlb is reserved > and a user need to opt out of it using crashkernel_low=0 if system has > iommu enabled. > > - crashkernel=X by default first looks for specified memory in low > memory area. > > I kind of like yinghai's approach. It is little wasteful of memory when > memory is reserved high but atleast user does not have know how much memory > to reserve low it works both when memory is reserved low (system does > not have any RAM mapped above 4G) and when memory is reserved high. > I would agree, I think it is the most user friendly. -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/