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

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Message-Id: <7c515276-81f0-8595-7deb-93ddbec6bb30@linux.vnet.ibm.com>
Date:   Wed, 10 May 2017 20:40:22 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     Michal Suchánek <msuchanek@...e.de>
Cc:     Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v4 RFT 1/2] powerpc/fadump: reduce memory consumption for
 capture kernel



On Wednesday 10 May 2017 08:28 PM, Michal Suchánek wrote:
> On Wed, 3 May 2017 12:43:33 +0530
> Hari Bathini <hbathini@...ux.vnet.ibm.com> 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=1
>> numa=off" is not resulting in the intended way..
> Since yaboot arguments are quoted you will probably want something like
>
> append = "quiet splash somearg1 somearg2 fadump_append=\"nr_cpus=1
> numa=off\""

I did try this out. But it wasn't helping either..

> in yaboot.conf
>
> Looking at the yaboot parser it seems to handle quoting of quotes so
> unlike your parser that does not handle quoting of commas it allows
> passing arbitrary arguments to both the normal kernel and the fadump
> kernel.

Will improve on v5 to ensure quotes are taken care of..

Thanks
Hari