Re: [patch 1/4] mm: memcontrol: inline memcg->move_lock locking

[Vladimir Davydov <vdavydov@parallels.com>]

On Tue, Oct 21, 2014 at 04:21:33PM -0400, Johannes Weiner wrote:
> The wrappers around taking and dropping the memcg->move_lock spinlock
> add nothing of value.  Inline the spinlock calls into the callsites.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Vladimir Davydov <vdavydov@parallels.com>

> ---
>  mm/memcontrol.c | 34 +++++++++-------------------------
>  1 file changed, 9 insertions(+), 25 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 293db8234179..1ff125d2a427 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1507,23 +1507,6 @@ static bool mem_cgroup_wait_acct_move(struct mem_cgroup *memcg)
>  	return false;
>  }
>  
> -/*
> - * Take this lock when
> - * - a code tries to modify page's memcg while it's USED.
> - * - a code tries to modify page state accounting in a memcg.
> - */
> -static void move_lock_mem_cgroup(struct mem_cgroup *memcg,
> -				  unsigned long *flags)
> -{
> -	spin_lock_irqsave(&memcg->move_lock, *flags);
> -}
> -
> -static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
> -				unsigned long *flags)
> -{
> -	spin_unlock_irqrestore(&memcg->move_lock, *flags);
> -}
> -
>  #define K(x) ((x) << (PAGE_SHIFT-10))
>  /**
>   * mem_cgroup_print_oom_info: Print OOM information relevant to memory controller.
> @@ -2013,7 +1996,7 @@ again:
>  		return;
>  	/*
>  	 * If this memory cgroup is not under account moving, we don't
> -	 * need to take move_lock_mem_cgroup(). Because we already hold
> +	 * need to take &memcg->move_lock. Because we already hold
>  	 * rcu_read_lock(), any calls to move_account will be delayed until
>  	 * rcu_read_unlock().
>  	 */
> @@ -2021,9 +2004,9 @@ again:
>  	if (atomic_read(&memcg->moving_account) <= 0)
>  		return;
>  
> -	move_lock_mem_cgroup(memcg, flags);
> +	spin_lock_irqsave(&memcg->move_lock, *flags);
>  	if (memcg != pc->mem_cgroup) {
> -		move_unlock_mem_cgroup(memcg, flags);
> +		spin_unlock_irqrestore(&memcg->move_lock, *flags);
>  		goto again;
>  	}
>  	*locked = true;
> @@ -2038,7 +2021,7 @@ void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
>  	 * lock is held because a routine modifies pc->mem_cgroup
>  	 * should take move_lock_mem_cgroup().
>  	 */
> -	move_unlock_mem_cgroup(pc->mem_cgroup, flags);
> +	spin_unlock_irqrestore(&pc->mem_cgroup->move_lock, *flags);
>  }
>  
>  void mem_cgroup_update_page_stat(struct page *page,
> @@ -3083,7 +3066,7 @@ static int mem_cgroup_move_account(struct page *page,
>  	if (pc->mem_cgroup != from)
>  		goto out_unlock;
>  
> -	move_lock_mem_cgroup(from, &flags);
> +	spin_lock_irqsave(&from->move_lock, flags);
>  
>  	if (!PageAnon(page) && page_mapped(page)) {
>  		__this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
> @@ -3107,7 +3090,8 @@ static int mem_cgroup_move_account(struct page *page,
>  
>  	/* caller should have done css_get */
>  	pc->mem_cgroup = to;
> -	move_unlock_mem_cgroup(from, &flags);
> +	spin_unlock_irqrestore(&from->move_lock, flags);
> +
>  	ret = 0;
>  
>  	local_irq_disable();
> @@ -6033,9 +6017,9 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
>  	 * but there might still be references, e.g. from finishing
>  	 * writeback.  Follow the charge moving protocol here.
>  	 */
> -	move_lock_mem_cgroup(memcg, &flags);
> +	spin_lock_irqsave(&memcg->move_lock, flags);
>  	pc->mem_cgroup = NULL;
> -	move_unlock_mem_cgroup(memcg, &flags);
> +	spin_unlock_irqrestore(&memcg->move_lock, flags);
>  
>  	if (lrucare)
>  		unlock_page_lru(oldpage, isolated);
> -- 
> 2.1.2
> 

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