mm/dynamic_hugetlb: establish the dynamic hugetlb feature framework

hulk inclusion
category: feature
bugzilla: 46904, https://gitee.com/openeuler/kernel/issues/I4QSHG


CVE: NA

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Dynamic hugetlb is a self-developed feature based on the hugetlb and memcontrol.
It supports to split huge page dynamically in a memory cgroup. There is a new structure
dhugetlb_pool in every mem_cgroup to manage the pages configured to the mem_cgroup.
For the mem_cgroup configured with dhugetlb_pool, processes in the mem_cgroup will
preferentially use the pages in dhugetlb_pool.

Dynamic hugetlb supports three types of pages, including 1G/2M huge pages and 4K pages.
For the mem_cgroup configured with dhugetlb_pool, processes will be limited to alloc
1G/2M huge pages only from dhugetlb_pool. But there is no such constraint for 4K pages.
If there are insufficient 4K pages in the dhugetlb_pool, pages can also be allocated from
buddy system. So before using dynamic hugetlb, user must know how many huge pages they
need.

Usage:
1. Add 'dynamic_hugetlb=on' in cmdline to enable dynamic hugetlb feature.
2. Prealloc some 1G hugepages through hugetlb.
3. Create a mem_cgroup and configure dhugetlb_pool to mem_cgroup.
4. Configure the count of 1G/2M hugepages, and the remaining pages in dhugetlb_pool will
   be used as basic pages.
5. Bound a process to mem_cgroup. then the memory for it will be allocated from dhugetlb_pool.

This patch add the corresponding structure dhugetlb_pool for dynamic hugetlb feature,
the interface 'dhugetlb.nr_pages' in mem_cgroup to configure dhugetlb_pool and the cmdline
'dynamic_hugetlb=on' to enable dynamic hugetlb feature.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>