From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from out02.mta.xmission.com ([166.70.13.232]) by merlin.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1fLtKJ-0002GW-D9 for kexec@lists.infradead.org; Thu, 24 May 2018 16:42:56 +0000 From: ebiederm@xmission.com (Eric W. Biederman) 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> <20180524014234.GA2031@dhcp-128-65.nay.redhat.com> Date: Thu, 24 May 2018 11:41:58 -0500 In-Reply-To: <20180524014234.GA2031@dhcp-128-65.nay.redhat.com> (Dave Young's message of "Thu, 24 May 2018 09:42:34 +0800") Message-ID: <87bmd53t0p.fsf@xmission.com> MIME-Version: 1.0 Subject: Re: [PATCH] kdump: add default crashkernel reserve kernel config options List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Dave Young Cc: dzickus@redhat.com, Neil Horman , Tony Luck , bhe@redhat.com, Michael Ellerman , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Hari Bathini , Benjamin Herrenschmidt , Martin Schwidefsky , Cong Wang , Andrew Morton , Anton Vorontsov , Ingo Molnar , Vivek Goyal Dave Young writes: > 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. Have you considered using the builtin command line aka CONFIG_CMDLINE? If as you are reserving a fixed amount of memory as your patch does that should be sufficient, and doable without any kernel changes. Eric _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec