mm: shmem: refactor thpsize_shmem_enabled_store() with sysfs_match_string()

Patch series "refactors thpsize_shmem_enabled_store() and
thpsize_shmem_enabled_show()", v4.

This patch (of 2):

Inspired by commit 82d9ff648c6c ("mm: huge_memory: refactor
anon_enabled_store() with set_anon_enabled_mode()"), refactor
thpsize_shmem_enabled_store() using sysfs_match_string().  This eliminates
the duplicated spin_lock/unlock(), set/clear_bit(), calls across all
branches, reducing code duplication.

Behavioral change:
Call start_stop_khugepaged() only when the mode actually changes.
If unchanged, call set_recommended_min_free_kbytes() to preserve
legacy watermark behavior. This avoids unnecessary khugepaged restarts.

Tested with selftests ./run_kselftest.sh -t mm:ksft_thp.sh,
all test cases passed.

Link: https://lore.kernel.org/20260525102700.68707-1-ranxiaokai627@163.com
Link: https://lore.kernel.org/20260525102700.68707-2-ranxiaokai627@163.com
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Lance Yang <lance.yang@linux.dev>
Acked-by: David Hildenbrand (arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index 77a3e28e51601e97f61e1988721fe3d7a3586f8d..748b135d04fb65f91c6d228ec1c92d9e6baccdbe 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5463,6 +5463,29 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
 struct kobj_attribute shmem_enabled_attr = __ATTR_RW(shmem_enabled);
 static DEFINE_SPINLOCK(huge_shmem_orders_lock);
 
+enum huge_mode {
+       HUGE_SHMEM_ENABLED_ALWAYS = 0,
+       HUGE_SHMEM_ENABLED_INHERIT,
+       HUGE_SHMEM_ENABLED_WITHIN_SIZE,
+       HUGE_SHMEM_ENABLED_ADVISE,
+       HUGE_SHMEM_ENABLED_NEVER,
+};
+
+static const char * const huge_mode_strings[] = {
+       [HUGE_SHMEM_ENABLED_ALWAYS]      = "always",
+       [HUGE_SHMEM_ENABLED_INHERIT]     = "inherit",
+       [HUGE_SHMEM_ENABLED_WITHIN_SIZE] = "within_size",
+       [HUGE_SHMEM_ENABLED_ADVISE]      = "advise",
+       [HUGE_SHMEM_ENABLED_NEVER]       = "never",
+};
+
+static unsigned long * const huge_mode_orders[] = {
+       [HUGE_SHMEM_ENABLED_ALWAYS]      = &huge_shmem_orders_always,
+       [HUGE_SHMEM_ENABLED_INHERIT]     = &huge_shmem_orders_inherit,
+       [HUGE_SHMEM_ENABLED_WITHIN_SIZE] = &huge_shmem_orders_within_size,
+       [HUGE_SHMEM_ENABLED_ADVISE]      = &huge_shmem_orders_madvise,
+};
+
 static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
                                          struct kobj_attribute *attr, char *buf)
 {
@@ -5483,63 +5506,53 @@ static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
        return sysfs_emit(buf, "%s\n", output);
 }
 
+static bool set_shmem_enabled_mode(int order, enum huge_mode mode)
+{
+       bool changed = false;
+       enum huge_mode idx;
+
+       spin_lock(&huge_shmem_orders_lock);
+       for (idx = 0; idx < ARRAY_SIZE(huge_mode_orders); idx++) {
+               if (idx == mode)
+                       changed |= !__test_and_set_bit(order, huge_mode_orders[idx]);
+               else
+                       changed |= __test_and_clear_bit(order, huge_mode_orders[idx]);
+       }
+       spin_unlock(&huge_shmem_orders_lock);
+
+       return changed;
+}
+
 static ssize_t thpsize_shmem_enabled_store(struct kobject *kobj,
                                           struct kobj_attribute *attr,
                                           const char *buf, size_t count)
 {
        int order = to_thpsize(kobj)->order;
-       ssize_t ret = count;
-
-       if (sysfs_streq(buf, "always")) {
-               spin_lock(&huge_shmem_orders_lock);
-               clear_bit(order, &huge_shmem_orders_inherit);
-               clear_bit(order, &huge_shmem_orders_madvise);
-               clear_bit(order, &huge_shmem_orders_within_size);
-               set_bit(order, &huge_shmem_orders_always);
-               spin_unlock(&huge_shmem_orders_lock);
-       } else if (sysfs_streq(buf, "inherit")) {
-               /* Do not override huge allocation policy with non-PMD sized mTHP */
-               if (shmem_huge == SHMEM_HUGE_FORCE && !is_pmd_order(order))
-                       return -EINVAL;
+       int mode;
 
-               spin_lock(&huge_shmem_orders_lock);
-               clear_bit(order, &huge_shmem_orders_always);
-               clear_bit(order, &huge_shmem_orders_madvise);
-               clear_bit(order, &huge_shmem_orders_within_size);
-               set_bit(order, &huge_shmem_orders_inherit);
-               spin_unlock(&huge_shmem_orders_lock);
-       } else if (sysfs_streq(buf, "within_size")) {
-               spin_lock(&huge_shmem_orders_lock);
-               clear_bit(order, &huge_shmem_orders_always);
-               clear_bit(order, &huge_shmem_orders_inherit);
-               clear_bit(order, &huge_shmem_orders_madvise);
-               set_bit(order, &huge_shmem_orders_within_size);
-               spin_unlock(&huge_shmem_orders_lock);
-       } else if (sysfs_streq(buf, "advise")) {
-               spin_lock(&huge_shmem_orders_lock);
-               clear_bit(order, &huge_shmem_orders_always);
-               clear_bit(order, &huge_shmem_orders_inherit);
-               clear_bit(order, &huge_shmem_orders_within_size);
-               set_bit(order, &huge_shmem_orders_madvise);
-               spin_unlock(&huge_shmem_orders_lock);
-       } else if (sysfs_streq(buf, "never")) {
-               spin_lock(&huge_shmem_orders_lock);
-               clear_bit(order, &huge_shmem_orders_always);
-               clear_bit(order, &huge_shmem_orders_inherit);
-               clear_bit(order, &huge_shmem_orders_within_size);
-               clear_bit(order, &huge_shmem_orders_madvise);
-               spin_unlock(&huge_shmem_orders_lock);
-       } else {
-               ret = -EINVAL;
-       }
+       mode = sysfs_match_string(huge_mode_strings, buf);
+       if (mode < 0)
+               return mode;
 
-       if (ret > 0) {
-               int err = start_stop_khugepaged();
+       /* Do not override huge allocation policy with non-PMD sized mTHP */
+       if (mode == HUGE_SHMEM_ENABLED_INHERIT &&
+           shmem_huge == SHMEM_HUGE_FORCE && !is_pmd_order(order))
+               return -EINVAL;
 
+       if (set_shmem_enabled_mode(order, mode)) {
+               int err = start_stop_khugepaged();
                if (err)
-                       ret = err;
+                       return err;
+       } else {
+               /*
+                * Recalculate watermarks even when the mode hasn't changed
+                * to preserve the legacy behavior, as this is always called
+                * inside start_stop_khugepaged().
+                */
+               set_recommended_min_free_kbytes();
        }
-       return ret;
+
+       return count;
 }
 
 struct kobj_attribute thpsize_shmem_enabled_attr =