by default, the sector map created under the sparse model now only extends to the last non-reserved page frame, any reserved page frames afterwards are ignored.
previously, sparse would attempt to create a smaller number of larger sectors on systems with lots of reserved memory, often causing an out-of-memory condition. the reserved memory ratio calculation now compares reserved memory to free memory, rather than to the address of the last byte in physical memory. this improved heuristic means sparse is now better at choosing an appropriate sector size, allowing sparse to operate on systems with high amounts of reserved memory.
allocating a large power-of-2 block with memblock may cause the base pointer of a region to exceed the limit pointer after it has been aligned during the free region scan in do_alloc().
* the page array now only extends up to the last non-reserved memory frame.
* rather than memset'ing the whole array to zero, we only initialise p_flags
for each page in vm_page_array_init, and then leave it to group_pages_into_block
to initialise the other parts of vm_page_t.
if kmalloc is called with count=N before vm_bootstrap is finished,
the request will be fulfilled using memblock_alloc.
if N is a power of 2, the returned pointer will be aligned to
an N-byte boundary.
caches with object size N, where N is a power of two, will naturally
align their objects on N-byte boundaries.
all other caches will align to an 8-byte boundary by default.
