linux-kernel - Re: Early boot panic on machine with lots of memory

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Date:	Thu, 21 Jun 2012 13:17:28 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, hpa@...ux.intel.com,
	linux-mm <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Early boot panic on machine with lots of memory

Hello, Yinghai.

On Tue, Jun 19, 2012 at 07:57:45PM -0700, Yinghai Lu wrote:
> if it is that case, that change could fix other problem problem too.
> --- during the one free reserved.regions could double the array.

Yeah, that sounds much more attractive to me too.  Some comments on
the patch tho.

>  /**
>   * memblock_double_array - double the size of the memblock regions array
>   * @type: memblock type of the regions array being doubled
> @@ -216,7 +204,7 @@ static int __init_memblock memblock_doub
>  
>  	/* Calculate new doubled size */
>  	old_size = type->max * sizeof(struct memblock_region);
> -	new_size = old_size << 1;
> +	new_size = PAGE_ALIGN(old_size << 1);

We definintely can use some comments explaining why we want page
alignment.  It's kinda subtle.

This is a bit confusing here because old_size is the proper size
without padding while new_size is page aligned size with possible
padding.  Maybe discerning {old|new}_alloc_size is clearer?  Also, I
think adding @new_cnt variable which is calculated together would make
the code easier to follow.  So, sth like,

	/* explain why page aligning is necessary */
	old_size = type->max * sizeof(struct memblock_region);
	old_alloc_size = PAGE_ALIGN(old_size);

	new_max = type->max << 1;
	new_size = new_max * sizeof(struct memblock_region);
	new_alloc_size = PAGE_ALIGN(new_size);

and use alloc_sizes for alloc/frees and sizes for everything else.

>  unsigned long __init free_low_memory_core_early(int nodeid)
>  {
>  	unsigned long count = 0;
> -	phys_addr_t start, end;
> +	phys_addr_t start, end, size;
>  	u64 i;
>  
> -	/* free reserved array temporarily so that it's treated as free area */
> -	memblock_free_reserved_regions();
> +	for_each_free_mem_range(i, MAX_NUMNODES, &start, &end, NULL)
> +		count += __free_memory_core(start, end);
>  
> -	for_each_free_mem_range(i, MAX_NUMNODES, &start, &end, NULL) {
> -		unsigned long start_pfn = PFN_UP(start);
> -		unsigned long end_pfn = min_t(unsigned long,
> -					      PFN_DOWN(end), max_low_pfn);
> -		if (start_pfn < end_pfn) {
> -			__free_pages_memory(start_pfn, end_pfn);
> -			count += end_pfn - start_pfn;
> -		}
> -	}
> +	/* free range that is used for reserved array if we allocate it */
> +	size = get_allocated_memblock_reserved_regions_info(&start);
> +	if (size)
> +		count += __free_memory_core(start, start + size);

I'm afraid this is too early.  We don't want the region to be unmapped
yet.  This should only happen after all memblock usages are finished
which I don't think is the case yet.

Thanks.

-- 
tejun
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