From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935417AbeEXBmw (ORCPT ); Wed, 23 May 2018 21:42:52 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:50394 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S935386AbeEXBmu (ORCPT ); Wed, 23 May 2018 21:42:50 -0400 Date: Thu, 24 May 2018 09:42:34 +0800 From: Dave Young To: "Eric W. Biederman" Cc: Andrew Morton , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, Cong Wang , Neil Horman , Ingo Molnar , Vivek Goyal , Tony Luck , Anton Vorontsov , Michael Ellerman , Benjamin Herrenschmidt , Martin Schwidefsky , Hari Bathini , dzickus@redhat.com, bhe@redhat.com Subject: Re: [PATCH] kdump: add default crashkernel reserve kernel config options Message-ID: <20180524014234.GA2031@dhcp-128-65.nay.redhat.com> References: <20180521025337.GA4627@dhcp-128-65.nay.redhat.com> <20180521120215.117d963a7619eb0d1f54bced@linux-foundation.org> <20180523070641.GA1689@dhcp-128-65.nay.redhat.com> <877enucqr0.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877enucqr0.fsf@xmission.com> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Eric, On 05/23/18 at 10:53am, Eric W. Biederman wrote: > Dave Young writes: > > > [snip] > > > >> > > >> > +config CRASHKERNEL_DEFAULT_THRESHOLD_MB > >> > + int "System memory size threshold for kdump memory default reserving" > >> > + depends on CRASH_CORE > >> > + default 0 > >> > + help > >> > + CRASHKERNEL_DEFAULT_MB is used as default crashkernel value if > >> > + the system memory size is equal or bigger than the threshold. > >> > >> "the threshold" is rather vague. Can it be clarified? > >> > >> In fact I'm really struggling to understand the logic here.... > >> > >> > >> > +config CRASHKERNEL_DEFAULT_MB > >> > + int "Default crashkernel memory size reserved for kdump" > >> > + depends on CRASH_CORE > >> > + default 0 > >> > + help > >> > + This is used as the default kdump reserved memory size in MB. > >> > + crashkernel=X kernel cmdline can overwrite this value. > >> > + > >> > config HAVE_IMA_KEXEC > >> > bool > >> > > >> > @@ -143,6 +144,24 @@ static int __init parse_crashkernel_simp > >> > return 0; > >> > } > >> > > >> > +static int __init get_crashkernel_default(unsigned long long system_ram, > >> > + unsigned long long *size) > >> > +{ > >> > + unsigned long long sz = CONFIG_CRASHKERNEL_DEFAULT_MB; > >> > + unsigned long long thres = CONFIG_CRASHKERNEL_DEFAULT_THRESHOLD_MB; > >> > + > >> > + thres *= SZ_1M; > >> > + sz *= SZ_1M; > >> > + > >> > + if (sz >= system_ram || system_ram < thres) { > >> > + pr_debug("crashkernel default size can not be used.\n"); > >> > + return -EINVAL; > >> > >> In other words, > >> > >> if (system_ram <= CONFIG_CRASHKERNEL_DEFAULT_MB || > >> system_ram < CONFIG_CRASHKERNEL_DEFAULT_THRESHOLD_MB) > >> fail; > >> > >> yes? > >> > >> How come? What's happening here? Perhaps a (good) explanatory comment > >> is needed. And clearer Kconfig text. > >> > >> All confused :( > > > > Andrew, I tuned it a bit, removed the check of sz >= system_ram, so if > > the size is too large and kernel can not find enough memory it will > > still fail in latter code. > > > > Is below version looks clearer? > > What is the advantage of providing this in a kconfig option rather > than on the kernel command line as we can now? It is not a replacement of the cmdline, this can be a supplement to the crashkernel command line. For a lot of common use cases if we have the auto reservation user just do not need to manually set the cmdline for example on a virtual machine and usual setup (except of the comlicate storage and very large machines). The crashkernel=auto has been used for long time, Red Hat QE tested it on a lot of different lab machines and proved it works well. Kdump usually just works so admin do little work to enable kdump. But the crashkernel=auto implementation has some drawbacks that is it is more like embed policy in the code and it is not flexible like a config option. Thanks Dave