Hi Linus, Andrew,

Here's a patch to allocate memory for big system hash tables with the bootmem
allocator rather than with main page allocator.

I've coelesced the meat of the inode and dentry allocation routines into one
such routine in mm/page_alloc.c that the the respective initialisation
functions now call before mem_init() is called.

This routine gets it's approximation of memory size by counting up the
ZONE_NORMAL and ZONE_DMA pages (and ZONE_HIGHMEM if requested) in all the
nodes passed to the main allocator by paging_init() (or wherever the arch does
it). It does not use max_low_pfn as that doesn't seem to be available on all
archs, and it doesn't use num_physpages since that includes highmem pages not
available to the kernel for allocating data structures upon - which may not be
appropriate when calculating hash table size.

On the off chance that the size of each hash bucket may not be exactly a power
of two, the routine will only allocate as many pages as is necessary to ensure
that the number of buckets is exactly a power of two, rather than allocating
the smallest power-of-two sized chunk of memory that will hold the same array
of buckets.

The maximum size of any single hash table is given by MAX_SYS_HASH_TABLE_ORDER,
as is now defined in linux/mmzone.h.

David