mm: huge_memory: refactor anon_enabled_store() with set_anon_enabled_mode()

mm: huge_memory: refactor anon_enabled_store() with set_anon_enabled_mode()

Consolidate the repeated spin_lock/set_bit/clear_bit pattern in
anon_enabled_store() into a new set_anon_enabled_mode() helper that loops
over an orders[] array, setting the bit for the selected mode and clearing
the others.

Introduce enum anon_enabled_mode and anon_enabled_mode_strings[] for the
per-order anon THP setting.

Use sysfs_match_string() with the anon_enabled_mode_strings[] table to
replace the if/else chain of sysfs_streq() calls.

The helper uses __test_and_set_bit()/__test_and_clear_bit() to track
whether the state actually changed, so start_stop_khugepaged() is only
called when needed.  When the mode is unchanged,
set_recommended_min_free_kbytes() is called directly to preserve the
watermark recalculation behavior of the original code.

Link: https://lkml.kernel.org/r/20260317-thp_logs-v7-2-31eb98fa5a8b@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>