From mboxrd@z Thu Jan 1 00:00:00 1970 From: "M. Mohan Kumar" Date: Tue, 25 Aug 2009 10:40:37 +0000 Subject: Re: [Patch 6/8] powerpc: add CONFIG_KEXEC_AUTO_RESERVE Message-Id: <20090825102837.GB14591@in.ibm.com> List-Id: References: <20090821065637.4855.32234.sendpatchset@localhost.localdomain> <20090821065739.4855.19179.sendpatchset@localhost.localdomain> <1251121443.10645.56.camel@concordia> <4A938348.2020306@redhat.com> In-Reply-To: <4A938348.2020306@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Amerigo Wang Cc: michael@ellerman.id.au, linux-kernel@vger.kernel.org, tony.luck@intel.com, linux-ia64@vger.kernel.org, Neil Horman , "Eric W. Biederman" , kamezawa.hiroyu@jp.fujitsu.com, Andi Kleen , akpm@linux-foundation.org, bernhard.walle@gmx.de, Fenghua Yu , Ingo Molnar , Anton Vorontsov On Tue, Aug 25, 2009 at 02:23:04PM +0800, Amerigo Wang wrote: > Michael Ellerman wrote: >> On Fri, 2009-08-21 at 02:55 -0400, Amerigo Wang wrote: >> >>> Introduce a new config option KEXEC_AUTO_RESERVE for powerpc. >>> >>> Index: linux-2.6/arch/powerpc/Kconfig >>> =================================>>> --- linux-2.6.orig/arch/powerpc/Kconfig >>> +++ linux-2.6/arch/powerpc/Kconfig >>> @@ -346,6 +346,17 @@ config KEXEC >>> support. As of this writing the exact hardware interface is >>> strongly in flux, so no good recommendation can be made. >>> +config KEXEC_AUTO_RESERVE >>> + bool "automatically reserve memory for kexec kernel" >>> + depends on KEXEC >>> + default y >>> + ---help--- >>> + Automatically reserve memory for a kexec kernel, so that you don't >>> + need to specify numbers for the "crashkernel=X@Y" boot option, >>> + instead you can use "crashkernel=auto". To make this work, you need >>> + to have more than 4G memory. On PPC, 256M is reserved, 1/32 memory >>> + on PPC64, but it will not exceed 1T/32. >>> >> >> To be honest I don't see why this logic goes in the kernel. It seems to >> me that it's policy how much memory you devote to the crash kernel vs >> the production kernel. It depends on what kind of crash kernel you're >> loading, a minimal UP dump kernel, or a full-featured SMP behemoth, An >> it depends on how much memory you're willing to leave idle in the >> off-chance you crash. >> > > True, but since in the crash kernel, we have very little memory, so > probably loading a full-featured SMP kernel doesn't make much sense... > > And in patch 1/8, I introduced a way to free the reserved memory at > run-time. > >> That aside, I don't see how this will be useful in practice, if it only >> works for memory sizes over 4G? Or are we saying that people with less >> than 4G don't need crash kernels? If we're not saying that, those users, >> or those users' distros, still need to do some logic to work out if they >> have < 4GB of memory and if so pick a crash kernel size. So why can't >> they pick the size in the > 4GB case also? >> > > No, we set 4G as a threshold because we only want this work when have > have enough memory which is defined as 4G currently... This can be > changed to arch-dependent, e.g. ppc. I am very open to this. > So the distro/admin have to use crashkernel=auto for machines having more than 4GB RAM and for machines with less than 4GB RAM they have to use the crashkernel=x@y (or extended crashkernel syntax)? IMHO it will be nice if crashkernel=auto could handle all of the situations. Regards, M. Mohan Kumar