mm/huge_memory.c: rework the function vma_adjust_trans_huge()

Patch series "Some cleanups for huge_memory", v3.

This series contains cleanups to rework some function logics to make it
more readable, use helper function and so on.  More details can be found
in the respective changelogs.

This patch (of 6):

The current implementation of vma_adjust_trans_huge() contains some
duplicated codes.  Add helper function to get rid of these codes to make
it more succinct.

Link: https://lkml.kernel.org/r/20210318122722.13135-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210318122722.13135-2-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Peter Xu <peterx@redhat.com>
Cc: yuleixzhang <yulei.kernel@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Thomas Hellstrm (Intel) <thomas_os@shipmail.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>