mm/dynamic_hugetlb: alloc huge pages from dhugetlb_pool

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


CVE: NA

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Add function to alloc huge page from dhugetlb_pool.
When process is bound to a mem_cgroup configured with dhugetlb_pool,
only allowed to alloc huge page from dhugetlb_pool. If there is no huge
pages in dhugetlb_pool, the mmap() will failed due to the reserve count
introduced in previous patch.

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