From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754316Ab1IFMAV (ORCPT ); Tue, 6 Sep 2011 08:00:21 -0400 Received: from e23smtp04.au.ibm.com ([202.81.31.146]:45734 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753590Ab1IFMAO (ORCPT ); Tue, 6 Sep 2011 08:00:14 -0400 Message-ID: <4E660B3B.3070608@linux.vnet.ibm.com> Date: Tue, 06 Sep 2011 17:29:55 +0530 From: Mahesh Jagannath Salgaonkar User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 MIME-Version: 1.0 To: Anton Blanchard CC: Benjamin Herrenschmidt , linuxppc-dev , Linux Kernel , Michael Ellerman , Milton Miller , "Eric W. Biederman" Subject: Re: [RFC PATCH 02/10] fadump: Reserve the memory for firmware assisted dump. References: <20110713180252.6210.34810.stgit@mars.in.ibm.com> <20110713180648.6210.39530.stgit@mars.in.ibm.com> <20110831141134.590c4f4e@kryten> In-Reply-To: <20110831141134.590c4f4e@kryten> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Anton, On 08/31/2011 09:41 AM, Anton Blanchard wrote: > > Hi Mahesh, > > Just a few comments. > >> +#define RMR_START 0x0 >> +#define RMR_END (0x1UL << 28) /* 256 MB */ > > What if the RMO is bigger than 256MB? Should we be using ppc64_rma_size? The idea was to have a minimum memory threshold that requires for a kernel to boot successfully. On some Power systems where RMO is 128MB, it still requires minimum of 256MB for kernel to boot successfully. I think we can rename above #defines as BOOT_MEM_START and BOOT_MEM_END respectively and have BOOT_MEM_END defined as below: #define BOOT_MEM_END ((ppc64_rma_size < (0x1UL << 28)) ? \ (0x1UL << 28) : ppc64_rma_size) What do you think? > >> +#ifdef DEBUG >> +#define PREFIX "fadump: " >> +#define DBG(fmt...) printk(KERN_ERR PREFIX fmt) >> +#else >> +#define DBG(fmt...) >> +#endif > > We should use the standard debug macros (pr_debug etc). Sure will do that. > >> +/* Global variable to hold firmware assisted dump configuration info. */ >> +static struct fw_dump fw_dump; > > You can remove this comment, especially because the variable isn't global :) Agree. > >> + sections = of_get_flat_dt_prop(node, "ibm,configure-kernel-dump-sizes", >> + NULL); >> + >> + if (!sections) >> + return 0; >> + >> + for (i = 0; i < FW_DUMP_NUM_SECTIONS; i++) { >> + switch (sections[i].dump_section) { >> + case FADUMP_CPU_STATE_DATA: >> + fw_dump.cpu_state_data_size = >> sections[i].section_size; >> + break; >> + case FADUMP_HPTE_REGION: >> + fw_dump.hpte_region_size = >> sections[i].section_size; >> + break; >> + } >> + } >> + return 1; >> +} > > This makes me a bit nervous. We should really get the size of the property > and use it to iterate through the array. I saw no requirement in the PAPR > that the array had to be 2 entries long. > Agree. Will make the change. >> +static inline unsigned long calculate_reserve_size(void) >> +{ >> + unsigned long size; >> + >> + /* divide by 20 to get 5% of value */ >> + size = memblock_end_of_DRAM(); >> + do_div(size, 20); >> + >> + /* round it down in multiples of 256 */ >> + size = size & ~0x0FFFFFFFUL; >> + >> + /* Truncate to memory_limit. We don't want to over reserve >> the memory.*/ >> + if (memory_limit && size > memory_limit) >> + size = memory_limit; >> + >> + return (size > RMR_END ? size : RMR_END); >> +} > > 5% is pretty aribitrary, that's 400GB on an 8TB box. Also our experience > with kdump is that 256MB is too small. Is there any reason to scale it > with memory size? Can we do what kdump does and set it to a single > value (eg 512MB)? I have picked up this heuristic from the phyp-assisted dump code. I am yet to figure out a fool-proof method to calculate the minimum memory needed for any Power box to successfully boot. Till then, I presume we can use this heuristic based approach? While testing these patches on huge power system with 1TB RAM and 896 CPUs, I found that even 512MB is small. Hence setting it to a single value may not work for all system configuration. > > We could override the default with a boot option, which is similar to > how kdump specifies the region to reserve. Agree, will work on the change. Thanks, -Mahesh.