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

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Message-Id: <cbe833de-8cf2-d868-7b6a-da2a7908976a@linux.vnet.ibm.com>
Date:   Tue, 2 May 2017 22:14:48 +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

Hi Michal,


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);
> +	}
> +
> +	return 0;
> +}
> +early_param("fadump_append", early_fadump_append_param);
> +
>   /* Look for fadump= cmdline option. */
>   static int __init early_fadump_param(char *p)
>   {

I don't think this addresses Michael's concern in v3..
IIUC, we should actually be editing boot_command_line early
in the boot process instead of using parse_early_options() to enforce
the additional parameters..

Thanks
Hari