linux-kernel - Re: [PATCH v4 RFT 1/2] powerpc/fadump: reduce memory consumption for capture kernel

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Message-Id: <c70b9fde-c3a1-751c-b69e-942d8a6b81af@linux.vnet.ibm.com>
Date:   Wed, 3 May 2017 14:19:19 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     Michal Suchanek <msuchanek@...e.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Jonathan Corbet <corbet@....net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.cz>, linuxppc-dev@...ts.ozlabs.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 RFT 1/2] powerpc/fadump: reduce memory consumption for
 capture kernel



On Wednesday 03 May 2017 12:43 PM, Hari Bathini wrote:
>
>
> On Tuesday 02 May 2017 09:26 PM, Michal Suchanek wrote:
>> With fadump (dump capture) kernel booting like a regular kernel, it 
>> almost
>> needs the same amount of memory to boot as the production kernel, 
>> which is
>> unwarranted for a dump capture kernel. But with no option to disable 
>> some
>> of the unnecessary subsystems in fadump kernel, that much memory is 
>> wasted
>> on fadump, depriving the production kernel of that memory.
>>
>> Introduce kernel parameter 'fadump_append=' that would take regular 
>> kernel
>> parameters to be appended when fadump is active.
>> This 'fadump_append=' parameter can be leveraged to pass parameters like
>> nr_cpus=1, cgroup_disable=memory and numa=off, to disable unwarranted
>> resources/subsystems.
>>
>> Also, ensure the log "Firmware-assisted dump is active" is printed early
>> in the boot process to put the subsequent fadump messages in context.
>>
>> Suggested-by: Michael Ellerman <mpe@...erman.id.au>
>> Signed-off-by: Hari Bathini <hbathini@...ux.vnet.ibm.com>
>> Signed-off-by: Michal Suchanek <msuchanek@...e.de>
>> ---
>> v4:
>>   - use space separated arguments instead of comma separated
>>   - do not append parameters when fadummp is disabled
>> ---
>>   arch/powerpc/kernel/fadump.c | 27 ++++++++++++++++++++++++---
>>   1 file changed, 24 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
>> index ebf2e9c..e0c728a 100644
>> --- a/arch/powerpc/kernel/fadump.c
>> +++ b/arch/powerpc/kernel/fadump.c
>> @@ -79,8 +79,10 @@ int __init early_init_dt_scan_fw_dump(unsigned 
>> long node,
>>        * dump data waiting for us.
>>        */
>>       fdm_active = of_get_flat_dt_prop(node, "ibm,kernel-dump", NULL);
>> -    if (fdm_active)
>> +    if (fdm_active) {
>> +        pr_info("Firmware-assisted dump is active.\n");
>>           fw_dump.dump_active = 1;
>> +    }
>>
>>       /* Get the sizes required to store dump data for the firmware 
>> provided
>>        * dump sections.
>> @@ -263,8 +265,12 @@ int __init fadump_reserve_mem(void)
>>   {
>>       unsigned long base, size, memory_boundary;
>>
>> -    if (!fw_dump.fadump_enabled)
>> +    if (!fw_dump.fadump_enabled) {
>> +        if (fw_dump.dump_active)
>> +            pr_warn("Firmware-assisted dump was active but kernel"
>> +                " booted with fadump disabled!\n");
>>           return 0;
>> +    }
>>
>>       if (!fw_dump.fadump_supported) {
>>           printk(KERN_INFO "Firmware-assisted dump is not supported on"
>> @@ -304,7 +310,6 @@ int __init fadump_reserve_mem(void)
>>           memory_boundary = memblock_end_of_DRAM();
>>
>>       if (fw_dump.dump_active) {
>> -        printk(KERN_INFO "Firmware-assisted dump is active.\n");
>>           /*
>>            * If last boot has crashed then reserve all the memory
>>            * above boot_memory_size so that we don't touch it until
>> @@ -363,6 +368,22 @@ unsigned long __init 
>> arch_reserved_kernel_pages(void)
>>       return memblock_reserved_size() / PAGE_SIZE;
>>   }
>>
>> +/* Look for fadump_append= cmdline option. */
>> +static int __init early_fadump_append_param(char *p)
>> +{
>> +    if (!p)
>> +        return 1;
>> +
>> +    if (fw_dump.fadump_enabled && fw_dump.dump_active) {
>> +    pr_info("enforcing additional parameters (%s) passed through "
>> +        "'fadump_append=' parameter\n", p);
>> +        parse_early_options(p);
>
> While testing this on a system with yaboot bootloader, it seems that 
> parsing
> a parameter with syntax like fadump_append="nr_cpus numa=off" is not

fadump_append="nr_cpus numa=off" should have read 
fadump_append="nr_cpus=1 numa=off".
Nonetheless, considering different environments this is supposed to 
work, I was trying to convey
comma-separated append list maybe better over space-separated one..

Thanks
Hari