Re: [PATCH 2/6] mm/swap: Introduce alternative per-cpu LRU cache locking

[Peter Zijlstra]

On Tue, Sep 21, 2021 at 06:13:20PM +0200, Nicolas Saenz Julienne wrote:
> +static inline void lru_cache_lock(struct lru_cache_locks *locks)
> +{
> +	if (static_branch_unlikely(&remote_pcpu_cache_access)) {
> +		/* Avoid migration between this_cpu_ptr() and spin_lock() */
> +		migrate_disable();
> +		spin_lock(this_cpu_ptr(&locks->spin));
> +	} else {
> +		local_lock(&locks->local);
> +	}
> +}

> +static inline void lru_cache_unlock(struct lru_cache_locks *locks)
> +{
> +	if (static_branch_unlikely(&remote_pcpu_cache_access)) {
> +		spin_unlock(this_cpu_ptr(&locks->spin));
> +		migrate_enable();
> +	} else {
> +		local_unlock(&locks->local);
> +	}
> +}

*why* use migrate_disable(), that's horrible!