Re: [PATCH 1/3] kdump: extend crashkernel=range:size to dynamically increase reservation size

[Baoquan He <bhe@redhat.com>]

On 10/24/17 at 01:31pm, Dave Young wrote:
> crashkernel=range:size syntax allows to reserve specified size for system
> with total memory fall into the specified range. For example:
> crashkernel=2G-3G:128M,3G-:256M reserves 128M for system with memory >=2G
> and memory <3G, and reserves 256M for system with memory >= 3G
> 
> In the above case 256M as a fixed value which can not fulfill very huge 
> systems with large memory and IO devices. As memory size increases usually
> minimum memory requirement for booting will also increase. It is nearly
> impossible for a kernel to run with a fixed limited memory size for all
> kinds of systems.
> 
> Thus extend the crashkernel=range:size to let user specify the scaling
> ratio in kernel cmdline like below:
> crashkernel=range:size^order, for example:
> crashkernel=2G-:128M^14 reserve 128M + (total_memory - 128M) >> 14
> for machines with over 2G memory.

Well, ah.., this look a little ugly and tricky. Leave this to other
reviewers to comment.

> 
> Also s/start-[end]/[start]-end/ in kernel-parameters.txt according to code
> 
> Signed-off-by: Dave Young <dyoung@redhat.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |   10 ++++--
>  Documentation/kdump/kdump.txt                   |    7 ++--
>  kernel/crash_core.c                             |   35 +++++++++++++++++++++---
>  3 files changed, 41 insertions(+), 11 deletions(-)
> 
> --- linux-x86.orig/kernel/crash_core.c
> +++ linux-x86/kernel/crash_core.c
> @@ -31,7 +31,7 @@ static unsigned char *vmcoreinfo_data_sa
>  /*
>   * This function parses command lines in the format
>   *
> - *   crashkernel=ramsize-range:size[,...][@offset]
> + *   crashkernel=ramsize-range:size[,...][@offset][^order]
>   *
>   * The function returns 0 on success and -EINVAL on failure.
>   */
> @@ -41,6 +41,7 @@ static int __init parse_crashkernel_mem(
>  					unsigned long long *crash_base)
>  {
>  	char *cur = cmdline, *tmp;
> +	bool infinite_end = false;
>  
>  	/* for each entry of the comma-separated list */
>  	do {
> @@ -93,13 +94,21 @@ static int __init parse_crashkernel_mem(
>  		/* match ? */
>  		if (system_ram >= start && system_ram < end) {
>  			*crash_size = size;
> +			if (end == ULLONG_MAX)
> +				infinite_end = true;
>  			break;
>  		}
>  	} while (*cur++ == ',');
>  
> -	if (*crash_size > 0) {
> -		while (*cur && *cur != ' ' && *cur != '@')
> +	if (*crash_size <= 0)
> +		goto out;
> +
> +	while (*cur && *cur != ' ') {
> +		if (*cur != '@' && *cur != '^') {
>  			cur++;
> +			continue;
> +		}
> +
>  		if (*cur == '@') {
>  			cur++;
>  			*crash_base = memparse(cur, &tmp);
> @@ -107,10 +116,28 @@ static int __init parse_crashkernel_mem(
>  				pr_warn("Memory value expected after '@'\n");
>  				return -EINVAL;
>  			}
> -		}
> +			cur = tmp;
> +		} else if (*cur == '^' && infinite_end ) {
> +			unsigned long long shift, size;
> +
> +			cur++;
> +			shift = memparse(cur, &tmp);
> +			if (cur == tmp) {
> +				pr_warn("Memory reservation scale order expected after '^'\n");
> +				return -EINVAL;
> +			}
> +			size = (system_ram - *crash_size) >> shift;
> +			size = *crash_size + roundup(size, 1ULL << 20);
> +			if (size < system_ram)
> +				*crash_size = size;
> +			cur = tmp;
> +		} else
> +			cur++;
>  	}
>  
>  	return 0;
> +out:
> +	return -EINVAL;
>  }
>  
>  /*
> --- linux-x86.orig/Documentation/admin-guide/kernel-parameters.txt
> +++ linux-x86/Documentation/admin-guide/kernel-parameters.txt
> @@ -680,12 +680,14 @@
>  			is selected automatically. Check
>  			Documentation/kdump/kdump.txt for further details.
>  
> -	crashkernel=range1:size1[,range2:size2,...][@offset]
> +	crashkernel=range1:size1[,range2:size2,...][@offset][^order]
>  			[KNL] Same as above, but depends on the memory
>  			in the running system. The syntax of range is
> -			start-[end] where start and end are both
> -			a memory unit (amount[KMG]). See also
> -			Documentation/kdump/kdump.txt for an example.
> +			[start]-end where start and end are both
> +			a memory unit (amount[KMG]). In case the end of the
> +			range is infinity '^order' can be used to scale
> +			the size to size + (total_mem - start) >> 2^order
> +			See also Documentation/kdump/kdump.txt for an example.
>  
>  	crashkernel=size[KMG],high
>  			[KNL, x86_64] range could be above 4G. Allow kernel
> --- linux-x86.orig/Documentation/kdump/kdump.txt
> +++ linux-x86/Documentation/kdump/kdump.txt
> @@ -267,19 +267,20 @@ been removed from the machine.
>  
>  The syntax is:
>  
> -    crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
> +    crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset][^order]
>      range=start-[end]
>  
>  For example:
>  
> -    crashkernel=512M-2G:64M,2G-:128M
> +    crashkernel=512M-2G:64M,2G-:128M^14
>  
>  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
> +    3) if the RAM size is larger than 2G, then reserve:
> +       128M + (total_mem - 128M) >> 14
>  
>  
>  
> 
>