Re: [PATCH v4 03/11] futex: Allow automatic allocation of process wide futex hash.

[Thomas Gleixner]

On Tue, Dec 03 2024 at 17:42, Sebastian Andrzej Siewior wrote:
> +static bool need_futex_hash_allocate_default(u64 clone_flags)
> +{
> +	if ((clone_flags & (CLONE_THREAD | CLONE_VM)) != (CLONE_THREAD | CLONE_VM))
> +		return false;
> +	if (!thread_group_empty(current))
> +		return false;
> +	if (current->mm->futex_hash_bucket)
> +		return false;

If you add an accessor like:

        if (mm_get_futex_hash_bucket(current->mm))

then you can either #ifdef the futex muck in mm_struct or make it

struct mm_futex_hash_bucket {
#ifdef CONFIG_FUTEX
	unsigned int			futex_hash_mask;
	struct futex_hash_bucket	*futex_hash_bucket;
#endif
};

and avoid the #ifdeffery in mm_struct itself because the empty struct
occupies zero space.

The accessor and the other helpers allow the the compiler to optimize
all of it out for CONFIG_FUTEX=n.

Thanks,

        tglx