I see 2 ways to do this. 

1. allocate 512 4KB contiguous pages everytime a handle_mm_fault is called and have the THP kernel thread to coalesce it to a huge page. 
2. modify the kernel (maybe extensively) to allocate 2MB page by default. 

I like 1. better because it requires less modifications. but it is not as reliable. any suggestions

Xin 



On Wed, Jul 30, 2014 at 2:57 PM, <Valdis.Kletnieks@vt.edu> wrote:
On Wed, 30 Jul 2014 14:41:26 -0500, Xin Tong said:

> Is there anyway for me to turn on HugePage by default in the Linux X86
> kernel, i.e. allocate a 2MB page by default in place of 4KB now ?

Possibly related config entries to research:

CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION=y
CONFIG_TRANSPARENT_HUGEPAGE=y
CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
# CONFIG_TRANSPARENT_HUGEPAGE_MADVISE is not set

However, if you allocate a single 4K page, that *won't* automatically
promote it to a hugepage - you need to allocate 2M of contiguous virtual
address space with the same access flags for it to coalesce into a hugepage.