Messages in this thread | | | Date | Tue, 06 Sep 2011 17:29:55 +0530 | From | Mahesh Jagannath Salgaonkar <> | Subject | Re: [RFC PATCH 02/10] fadump: Reserve the memory for firmware assisted dump. |
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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.
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