Re: Crash while mapping memory in pagetable_init() (Was: Re: .config)

H. Peter Anvin
2007-04-13T20:37:39Z

H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
>> H. Peter Anvin wrote:
>>> Really (pae ? 2M : 1M), in other words, plus the 128K for bootmem.
>>> Note that this is creating page tables for, not erasing. To map 2M,
>>> we will only use 2K of additional memory (meaning there is 50% chance
>>> we end up using an additional 4K page.)
>>>
>>> So the solution is simply to change INIT_MAP_BEYOND_END in head.S
>>> appropriately.
>> Like this? Should we bother adding some slop pages for allocations
>> which happen before paging_init()?
>
> Yes, although it really should be sensitive to CONFIG_X86_PAE.
>
>>
>> /*
>> * This is how much memory *in addition to the memory covered up to
>> - * and including _end* we need mapped initially. We need one bit for
>> - * each possible page, but only in low memory, which means
>> - * 2^32/4096/8 = 128K worst case (4G/4G split.)
>> + * and including _end* we need mapped initially.
>> + * We need:
>> + * - one bit for each possible page, but only in low memory, which
>> means
>> + * 2^32/4096/8 = 128K worst case (4G/4G split.)
>> + * - enough space to map all low memory, which means
>> + * (2^32/4096) / 512 + 4 pages (worst case for PAE)
>> *
>> * Modulo rounding, each megabyte assigned here requires a kilobyte of
>> * memory, which is currently unreclaimed.
>> *
>> * This should be a multiple of a page.
>> */
>> -#define INIT_MAP_BEYOND_END (128*1024)
>> +#define INIT_MAP_BEYOND_END (128*1024 + (2048 + 4)*4096)
>
> I suggest, for clarity and to minimize bloat:
>
> #ifdef CONFIG_X86_PAE
> # define PAGE_TABLE_SIZE ((2048+4)*4096)
> #else
> # define PAGE_TABLE_SIZE ((1024+1)*4096)
> #endif
>
> #define BOOTMEM_SIZE (128*1024)
>
> #define INIT_MAP_BEYOND_END (BOOTMEM_SIZE+PAGE_TABLE_SIZE)
>

Actually, better yet; there is no reason for these to be macros:

#ifdef CONFIG_X86_PAE
PAGE_TABLE_SIZE = (2048+4)*4096
#else
PAGE_TABLE_SIZE = (1024+1)*4096
#endif
BOOTMEM_SIZE = 128*1024

INIT_MAP_BEYOND_END = BOOTMEM_SIZE + PAGE_TABLE_SIZE

-hpa