Re: [PATCH v2 1/1] kernel/crash_core: Add crashkernel=auto for vmcore creation

[Dave Young]

Hi Saeed,
On 02/03/21 at 04:43pm, Saeed Mirzamohammadi wrote:
> This adds crashkernel=auto feature to configure reserved memory for
> vmcore creation. CONFIG_CRASH_AUTO_STR is defined to be set for
> different kernel distributions and different archs based on their
> needs.
> 
> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx>
> Signed-off-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> Tested-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> ---
>  Documentation/admin-guide/kdump/kdump.rst |  5 +++++
>  arch/Kconfig                              | 24 +++++++++++++++++++++++
>  kernel/crash_core.c                       |  7 +++++++
>  3 files changed, 36 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index 75a9dd98e76e..f95a2af64f59 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -285,7 +285,12 @@ This would mean:
>      2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
>      3) if the RAM size is larger than 2G, then reserve 128M
>  
> +Or you can use crashkernel=auto if you have enough memory. The threshold
> +is 1G on x86_64 and arm64. If your system memory is less than the threshold,
> +crashkernel=auto will not reserve memory. The size changes according to
> +the system memory size like below:
>  
> +    x86_64/arm64: 1G-64G:128M,64G-1T:256M,1T-:512M

This part should be updated since you do not make the default value arch
dependent.

The format of the auto str is documented well in kernel-parameters.txt
below part:
crashkernel=range1:size1[,range2:size2,...][@offset]

The crashkernel=auto should be also documented in kernel-parameters.txt
and do not need to explain the threshold etc again, just refer to the
"crashkernel=range1:size1[,range2:size2,...][@offset]" format would be
fine.

>  
>  Boot into System Kernel
>  =======================
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 56b6ccc0e32d..a772eb397d73 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -14,6 +14,30 @@ menu "General architecture-dependent options"
>  config CRASH_CORE
>  	bool
>  
> +if CRASH_CORE
> +
> +config CRASH_AUTO_STR
> +	string "Memory reserved for crash kernel"
> +	depends on CRASH_CORE
> +	default "1G-64G:128M,64G-1T:256M,1T-:512M"
> +	help
> +	  This configures the reserved memory dependent
> +	  on the value of System RAM. The syntax is:
> +	  crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
> +	              range=start-[end]
> +
> +	  For example:
> +	      crashkernel=512M-2G:64M,2G-:128M
> +
> +	  This would mean:
> +
> +	      1) if the RAM is smaller than 512M, then don't reserve anything
> +	         (this is the "rescue" case)
> +	      2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
> +	      3) if the RAM size is larger than 2G, then reserve 128M
> +
> +endif # CRASH_CORE
> +
>  config KEXEC_CORE
>  	select CRASH_CORE
>  	bool
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 106e4500fd53..ab0a2b4b1ffa 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -7,6 +7,7 @@
>  #include <linux/crash_core.h>
>  #include <linux/utsname.h>
>  #include <linux/vmalloc.h>
> +#include <linux/kexec.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -250,6 +251,12 @@ static int __init __parse_crashkernel(char *cmdline,
>  	if (suffix)
>  		return parse_crashkernel_suffix(ck_cmdline, crash_size,
>  				suffix);
> +#ifdef CONFIG_CRASH_AUTO_STR
> +	if (strncmp(ck_cmdline, "auto", 4) == 0) {
> +		ck_cmdline = CONFIG_CRASH_AUTO_STR;
> +		pr_info("Using crashkernel=auto, the size chosen is a best effort estimation.\n");
> +	}
> +#endif
>  	/*
>  	 * if the commandline contains a ':', then that's the extended
>  	 * syntax -- if not, it must be the classic syntax
> -- 
> 2.27.0
> 

Thanks
Dave