mm: huge_memory: use sysfs_match_string() in defrag_store()

mm: huge_memory: use sysfs_match_string() in defrag_store()

Patch series "mm: huge_memory: clean up defrag sysfs with shared", v2.

Refactor defrag_store() and defrag_show() to use shared data tables
instead of duplicated if/else chains.

Patch 1 introduces an enum defrag_mode, a defrag_mode_strings[] table, and
a defrag_flags[] mapping array, then rewrites defrag_store() to use
sysfs_match_string() with a loop over defrag_flags[].

Patch 2 refactors defrag_show() to use the same arrays, replacing its
hardcoded if/else chain of test_bit() calls and string literals.

This follows the same pattern applied to anon_enabled_store() in commit
522dfb4ba71f ("mm: huge_memory: refactor anon_enabled_store() with
change_anon_orders()").

This patch (of 2):

Replace the if/else chain of sysfs_streq() calls in defrag_store() with
sysfs_match_string() and a defrag_mode_strings[] table.

Introduce enum defrag_mode and defrag_flags[] array mapping each mode to
its corresponding transparent_hugepage_flag.  The store function now loops
over defrag_flags[], setting the bit for the selected mode and clearing
the others.  When mode is DEFRAG_NEVER (index 4), no index in the
4-element defrag_flags[] matches, so all flags are cleared.

Note that the enum ordering (always, defer, defer+madvise, madvise, never)
differs from the original if/else chain order in defrag_store() (always,
defer+madvise, defer, madvise, never).  This is intentional to match the
display order used by defrag_show().

This is a follow-up cleanup to commit 522dfb4ba71f ("mm: huge_memory:
refactor anon_enabled_store() with change_anon_orders()") which applied
the same sysfs_match_string() pattern to anon_enabled_store().

Link: https://lore.kernel.org/20260408-thp_defrag-v2-0-bc544c1bde4e@debian.org
Link: https://lore.kernel.org/20260408-thp_defrag-v2-1-bc544c1bde4e@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>