From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qc0-f173.google.com (mail-qc0-f173.google.com [209.85.216.173]) by kanga.kvack.org (Postfix) with ESMTP id 5C95F6B0031 for ; Tue, 14 Jan 2014 06:02:31 -0500 (EST) Received: by mail-qc0-f173.google.com with SMTP id i8so3994675qcq.4 for ; Tue, 14 Jan 2014 03:02:31 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTP id ge8si184833qab.146.2014.01.14.03.02.29 for ; Tue, 14 Jan 2014 03:02:30 -0800 (PST) Message-ID: <52D51938.1090408@redhat.com> Date: Tue, 14 Jan 2014 06:02:16 -0500 From: Prarit Bhargava MIME-Version: 1.0 Subject: Re: [PATCH 2/2] x86, e820 disable ACPI Memory Hotplug if memory mapping is specified by user [v2] References: <1389380698-19361-1-git-send-email-prarit@redhat.com> <1389380698-19361-4-git-send-email-prarit@redhat.com> <52D32962.5050908@redhat.com> <52D4793E.8070102@redhat.com> <1389659632.1792.247.camel@misato.fc.hp.com> In-Reply-To: <1389659632.1792.247.camel@misato.fc.hp.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Toshi Kani Cc: KOSAKI Motohiro , Bodo Eggert <7eggert@gmx.de>, LKML , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , the arch/x86 maintainers , Len Brown , "Rafael J. Wysocki" , Linn Crosetto , Pekka Enberg , Yinghai Lu , Andrew Morton , Tang Chen , Wen Congyang , Vivek Goyal , dyoung@redhat.com, linux-acpi@vger.kernel.org, "linux-mm@kvack.org" On 01/13/2014 07:33 PM, Toshi Kani wrote: > On Mon, 2014-01-13 at 18:39 -0500, Prarit Bhargava wrote: >> >> On 01/13/2014 03:31 PM, KOSAKI Motohiro wrote: >>> On Sun, Jan 12, 2014 at 6:46 PM, Prarit Bhargava wrote: >>>> >>>> >>>> On 01/11/2014 11:35 AM, 7eggert@gmx.de wrote: >>>>> >>>>> >>>>> On Fri, 10 Jan 2014, Prarit Bhargava wrote: >>>>> >>>>>> kdump uses memmap=exactmap and mem=X values to configure the memory >>>>>> mapping for the kdump kernel. If memory is hotadded during the boot of >>>>>> the kdump kernel it is possible that the page tables for the new memory >>>>>> cause the kdump kernel to run out of memory. >>>>>> >>>>>> Since the user has specified a specific mapping ACPI Memory Hotplug should be >>>>>> disabled in this case. >>>>> >>>>> I'll ask just in case: Is it possible to want memory hotplug in spite of >>>>> using memmap=exactmap or mem=X? >>>> >>>> Good question -- I can't think of a case. When a user specifies "memmap" or >>>> "mem" IMO they are asking for a very specific memory configuration. Having >>>> extra memory added above what the user has specified seems to defeat the purpose >>>> of "memmap" and "mem". >>> >>> May be yes, may be no. >>> >>> They are often used for a wrokaround to avoid broken firmware issue. >>> If we have no way >>> to explicitly enable hotplug. We will lose a workaround. >>> >>> Perhaps, there is no matter. Today, memory hotplug is only used on >>> high-end machine >>> and their firmware is carefully developped and don't have a serious >>> issue almostly. Though. >> >> Oof -- sorry Kosaki :( I didn't see this until just now (and your subsequent >> ACK on the updated patch). >> >> I just remembered that we did have a processor vendor's whitebox that would not >> boot unless we specified a specific memmap and we did specify memmap=exactmap to >> boot the system correctly and the system had hotplug memory. >> >> So it means that I should not key off of "memmap=exactmap". > > I do not think it makes sense. You needed memmap=exactmap as a > workaround because the kernel did not boot with the firmware's memory > info. So, it's broken, and you requested the kernel to ignore the > firmware info. > > Why do you think memory hotplug needs to be supported under such > condition, which has to use the broken firmware info? There was a memory address region that was not in the e820 map that had to be reserved for a specific device's use. It was not so we used memmap=exactmap and other memmap entries to "rewrite" the e820 map to see if the system would boot; then I filed a bug against the hardware vendor ;) So, yes, in that case I did want memory hotplug & memmap=exactmap. Admittedly this was a rare corner case, and I certainly could have recompiled the kernel. P. > > Thanks, > -Toshi > > > -- 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