Re: [PATCH v5 2/4] mm: huge_memory: refactor anon_enabled_store() with change_anon_orders()

[Wei Yang <richard.weiyang@gmail.com>]

On Tue, Mar 10, 2026 at 10:57:08AM -0700, Breno Leitao wrote:
>Consolidate the repeated spin_lock/set_bit/clear_bit pattern in
>anon_enabled_store() into a new change_anon_orders() 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.
>
>Signed-off-by: Breno Leitao <leitao@debian.org>
>Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
>---
> mm/huge_memory.c | 84 +++++++++++++++++++++++++++++++++++---------------------
> 1 file changed, 52 insertions(+), 32 deletions(-)
>
>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>index 8e2746ea74adf..e19dda5aaf195 100644
>--- a/mm/huge_memory.c
>+++ b/mm/huge_memory.c
>@@ -316,6 +316,20 @@ static ssize_t enabled_show(struct kobject *kobj,
> 	return sysfs_emit(buf, "%s\n", output);
> }
> 
>+enum anon_enabled_mode {
>+	ANON_ENABLED_ALWAYS	= 0,
>+	ANON_ENABLED_MADVISE	= 1,
>+	ANON_ENABLED_INHERIT	= 2,
>+	ANON_ENABLED_NEVER	= 3,
>+};
>+
>+static const char * const anon_enabled_mode_strings[] = {
>+	[ANON_ENABLED_ALWAYS]	= "always",
>+	[ANON_ENABLED_MADVISE]	= "madvise",
>+	[ANON_ENABLED_INHERIT]	= "inherit",
>+	[ANON_ENABLED_NEVER]	= "never",
>+};
>+

Just one trivial thing, maybe keep the sequence as the sysfs output?

Currently the output of /sys/kernel/transparent_hugepage/hugepages-xxxkB is

    always inherit madvise [never]

But no strong opinion on this.

> static ssize_t enabled_store(struct kobject *kobj,
> 			     struct kobj_attribute *attr,
> 			     const char *buf, size_t count)
>@@ -515,48 +529,54 @@ static ssize_t anon_enabled_show(struct kobject *kobj,
> 	return sysfs_emit(buf, "%s\n", output);
> }
> 
>+static bool set_anon_enabled_mode(int order, enum anon_enabled_mode mode)
>+{
>+	static unsigned long *enabled_orders[] = {
>+		&huge_anon_orders_always,
>+		&huge_anon_orders_madvise,
>+		&huge_anon_orders_inherit,
>+	};
>+	enum anon_enabled_mode m;
>+	bool changed = false;
>+
>+	spin_lock(&huge_anon_orders_lock);
>+	for (m = 0; m < ARRAY_SIZE(enabled_orders); m++) {
>+		if (m == mode)
>+			changed |= !__test_and_set_bit(order, enabled_orders[m]);
>+		else
>+			changed |= __test_and_clear_bit(order, enabled_orders[m]);
>+	}
>+	spin_unlock(&huge_anon_orders_lock);
>+
>+	return changed;
>+}
>+

Nice cleanup, so

Reviewed-by: Wei Yang <richard.weiyang@gmail.com>

> static ssize_t anon_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;
>+	int mode;
> 
>-	if (sysfs_streq(buf, "always")) {
>-		spin_lock(&huge_anon_orders_lock);
>-		clear_bit(order, &huge_anon_orders_inherit);
>-		clear_bit(order, &huge_anon_orders_madvise);
>-		set_bit(order, &huge_anon_orders_always);
>-		spin_unlock(&huge_anon_orders_lock);
>-	} else if (sysfs_streq(buf, "inherit")) {
>-		spin_lock(&huge_anon_orders_lock);
>-		clear_bit(order, &huge_anon_orders_always);
>-		clear_bit(order, &huge_anon_orders_madvise);
>-		set_bit(order, &huge_anon_orders_inherit);
>-		spin_unlock(&huge_anon_orders_lock);
>-	} else if (sysfs_streq(buf, "madvise")) {
>-		spin_lock(&huge_anon_orders_lock);
>-		clear_bit(order, &huge_anon_orders_always);
>-		clear_bit(order, &huge_anon_orders_inherit);
>-		set_bit(order, &huge_anon_orders_madvise);
>-		spin_unlock(&huge_anon_orders_lock);
>-	} else if (sysfs_streq(buf, "never")) {
>-		spin_lock(&huge_anon_orders_lock);
>-		clear_bit(order, &huge_anon_orders_always);
>-		clear_bit(order, &huge_anon_orders_inherit);
>-		clear_bit(order, &huge_anon_orders_madvise);
>-		spin_unlock(&huge_anon_orders_lock);
>-	} else
>-		ret = -EINVAL;
>+	mode = sysfs_match_string(anon_enabled_mode_strings, buf);
>+	if (mode < 0)
>+		return -EINVAL;
> 
>-	if (ret > 0) {
>-		int err;
>+	if (set_anon_enabled_mode(order, mode)) {
>+		int err = start_stop_khugepaged();
> 
>-		err = start_stop_khugepaged();
> 		if (err)
>-			ret = err;
>+			return err;
>+	} else {
>+		/*
>+		 * Recalculate watermarks even when the mode didn't
>+		 * change, as the previous code always called
>+		 * start_stop_khugepaged() which does this internally.
>+		 */
>+		set_recommended_min_free_kbytes();
> 	}
>-	return ret;
>+
>+	return count;
> }
> 
> static struct kobj_attribute anon_enabled_attr =
>
>-- 
>2.52.0
>

-- 
Wei Yang
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