[PATCH v2 2/2] powerpc/fadump: merge adjacent memory ranges to reduce PT_LOAD segements

[Mahesh Jagannath Salgaonkar]

On 08/07/2018 02:12 AM, Hari Bathini wrote:
> With dynamic memory allocation support for crash memory ranges array,
> there is no hard limit on the no. of crash memory ranges kernel could
> export, but program headers count could overflow in the /proc/vmcore
> ELF file while exporting each memory range as PT_LOAD segment. Reduce
> the likelihood of a such scenario, by folding adjacent crash memory
> ranges which minimizes the total number of PT_LOAD segments.
> 
> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
> ---
>  arch/powerpc/kernel/fadump.c |   45 ++++++++++++++++++++++++++++++++++--------
>  1 file changed, 36 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index 2ec5704..cd0c555 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -908,22 +908,41 @@ static int allocate_crash_memory_ranges(void)
>  static inline int fadump_add_crash_memory(unsigned long long base,
>  					  unsigned long long end)
>  {
> +	u64  start, size;
> +	bool is_adjacent = false;
> +
>  	if (base == end)
>  		return 0;
>  
> -	if (crash_mem_ranges == max_crash_mem_ranges) {
> -		int ret;
> +	/*
> +	 * Fold adjacent memory ranges to bring down the memory ranges/
> +	 * PT_LOAD segments count.
> +	 */
> +	if (crash_mem_ranges) {
> +		start = crash_memory_ranges[crash_mem_ranges-1].base;
> +		size = crash_memory_ranges[crash_mem_ranges-1].size;
>  
> -		ret = allocate_crash_memory_ranges();
> -		if (ret)
> -			return ret;
> +		if ((start + size) == base)
> +			is_adjacent = true;
> +	}
> +	if (!is_adjacent) {
> +		/* resize the array on reaching the limit */
> +		if (crash_mem_ranges == max_crash_mem_ranges) {
> +			int ret;
> +
> +			ret = allocate_crash_memory_ranges();
> +			if (ret)
> +				return ret;
> +		}
> +
> +		start = base;
> +		crash_memory_ranges[crash_mem_ranges].base = start;
> +		crash_mem_ranges++;
>  	}
>  
> +	crash_memory_ranges[crash_mem_ranges-1].size = (end - start);
>  	pr_debug("crash_memory_range[%d] [%#016llx-%#016llx], %#llx bytes\n",
> -		crash_mem_ranges, base, end - 1, (end - base));
> -	crash_memory_ranges[crash_mem_ranges].base = base;
> -	crash_memory_ranges[crash_mem_ranges].size = end - base;
> -	crash_mem_ranges++;
> +		(crash_mem_ranges - 1), start, end - 1, (end - start));
>  	return 0;
>  }
>  
> @@ -999,6 +1018,14 @@ static int fadump_setup_crash_memory_ranges(void)
>  
>  	pr_debug("Setup crash memory ranges.\n");
>  	crash_mem_ranges = 0;
> +
> +	/* allocate memory for crash memory ranges for the first time */
> +	if (!max_crash_mem_ranges) {
> +		ret = allocate_crash_memory_ranges();
> +		if (ret)
> +			return ret;
> +	}
> +

I see that the check for (!is_adjacent) in first hunk already handles
the first time allocation. Do we need this ?

Rest looks fine to me.

Reviewed-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>

Thanks,
-Mahesh.

>  	/*
>  	 * add the first memory chunk (RMA_START through boot_memory_size) as
>  	 * a separate memory chunk. The reason is, at the time crash firmware
>