mm/khugepaged: remove redundant clearing of struct collapse_control

Patch series "unify PMD scan results and remove redundant cleanup", v2.

This small series addresses two minor cleanup opportunities in the
hugepage collapse logic.

The initial motivation arose during a code review of madvise_collapse(),
where it was noted that the function was missing a handler for
SCAN_PMD_NONE.  This oversight exposed the inconsistent handling of
SCAN_PMD_NULL and SCAN_PMD_NONE.

Since both scan results are functionally identical (they indicate the
absence of a PTE table), the primary patch unifies them into a single,
clearer identifier, SCAN_NO_PTE_TABLE.

The series also takes the opportunity to remove a redundant clearing of
the struct collapse_control.


This patch (of 3):

The structure struct collapse_control is being unnecessarily cleared twice
during the huge page collapse process.

Both hpage_collapse_scan_file() and hpage_collapse_scan_pmd() currently
perform a clear operation on this structure.

Remove the redundant clear operation.

Link: https://lkml.kernel.org/r/20251114030028.7035-1-richard.weiyang@gmail.com
Link: https://lkml.kernel.org/r/20251114030028.7035-2-richard.weiyang@gmail.com


Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Nico Pache <npache@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>