Re: [PATCH v2 2/3] mm: huge_memory: refactor anon_enabled_store() with change_anon_orders()

[Lorenzo Stoakes (Oracle)]

On Thu, Mar 05, 2026 at 06:04:54AM -0800, 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 enabled_mode and enabled_mode_strings[] to be shared
> with enabled_store() in a subsequent patch.
>
> Use sysfs_match_string() with the 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@xxxxxxxxxx>

This is nice, you've improved my idea :)

I know you change another instance of this in 3/3, but I wonder if there are
other cases like this in the THP code we can fixup too?

Anyway, passing tests locally and LGTM so:

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>


> ---
>  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..19619213f54d1 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 enabled_mode {
> +	ENABLED_ALWAYS,
> +	ENABLED_MADVISE,
> +	ENABLED_INHERIT,
> +	ENABLED_NEVER,
> +};
> +
> +static const char * const enabled_mode_strings[] = {
> +	[ENABLED_ALWAYS]	= "always",
> +	[ENABLED_MADVISE]	= "madvise",
> +	[ENABLED_INHERIT]	= "inherit",
> +	[ENABLED_NEVER]		= "never",
> +};
> +
>  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 change_anon_orders(int order, enum enabled_mode mode)
> +{
> +	static unsigned long *orders[] = {
> +		&huge_anon_orders_always,
> +		&huge_anon_orders_madvise,
> +		&huge_anon_orders_inherit,
> +	};
> +	bool changed = false;
> +	int i;
> +
> +	spin_lock(&huge_anon_orders_lock);
> +	for (i = 0; i < ARRAY_SIZE(orders); i++) {
> +		if (i == mode)
> +			changed |= !test_and_set_bit(order, orders[i]);
> +		else
> +			changed |= test_and_clear_bit(order, orders[i]);
> +	}
> +	spin_unlock(&huge_anon_orders_lock);
> +
> +	return changed;
> +}
> +
>  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(enabled_mode_strings, buf);
> +	if (mode < 0)
> +		return -EINVAL;
>
> -	if (ret > 0) {
> -		int err;
> +	if (change_anon_orders(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 =
>
> --
> 2.47.3
>