[PATCH -V8 07/21] swap: Support PMD swap mapping in split_swap_cluster()

When splitting a THP in swap cache or failing to allocate a THP when swapin a huge swap cluster, the huge swap cluster will be split. In addition to clear the huge flag of the swap cluster, the PMD swap mapping count recorded in cluster_count() will be set to 0. But we will not touch PMD swap

[PATCH -V8 07/21] swap: Support PMD swap mapping in split_swap_cluster()

When splitting a THP in swap cache or failing to allocate a THP when swapin a huge swap cluster, the huge swap cluster will be split. In addition to clear the huge flag of the swap cluster, the PMD swap mapping count recorded in cluster_count() will be set to 0. But we will not touch PMD swap