mm/migration: remove unneeded local variable mapping_locked

mm/migration: remove unneeded local variable mapping_locked

Patch series "A few cleanup and fixup patches for migration", v2.

This series contains a few patches to remove unneeded variables, jump
label and use helper to simplify the code.  Also we fix some bugs such as
page refcounts leak , invalid node access and so on.  More details can be
found in the respective changelogs.

This patch (of 11):

When mapping_locked is true, TTU_RMAP_LOCKED is always set to ttu.  We can
check ttu instead so mapping_locked can be removed.  And ttu is either 0
or TTU_RMAP_LOCKED now.  Change '|=' to '=' to reflect this.

Link: https://lkml.kernel.org/r/20220318111709.60311-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20220318111709.60311-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>