Re: [RFC PATCH 3/3] memcg-v1: remove memcg move locking code

[Michal Hocko <mhocko@suse.com>]

On Wed 23-10-24 23:57:12, Shakeel Butt wrote:
> The memcg v1's charge move feature has been deprecated. There is no need
> to have any locking or protection against the moving charge. Let's
> proceed to remove all the locking code related to charge moving.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
> ---
> -/**
> - * folio_memcg_lock - Bind a folio to its memcg.
> - * @folio: The folio.
> - *
> - * This function prevents unlocked LRU folios from being moved to
> - * another cgroup.
> - *
> - * It ensures lifetime of the bound memcg.  The caller is responsible
> - * for the lifetime of the folio.
> - */
> -void folio_memcg_lock(struct folio *folio)
> -{
> -	struct mem_cgroup *memcg;
> -	unsigned long flags;
> -
> -	/*
> -	 * The RCU lock is held throughout the transaction.  The fast
> -	 * path can get away without acquiring the memcg->move_lock
> -	 * because page moving starts with an RCU grace period.
> -         */
> -	rcu_read_lock();

Is it safe to remove the implicit RCU?

-- 
Michal Hocko
SUSE Labs