Re: [PATCH V2 2/3] memcg: alter mem_cgroup_{update,inc,dec}_page_stat() args to memcg pointer

[Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>]

(2013/05/13 14:05), Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org>
> 
> Change the first argument of mem_cgroup_{update,inc,dec}_page_stat() from
> 'struct page *' to 'struct mem_cgroup *', and so move PageCgroupUsed(pc)
> checking out of mem_cgroup_update_page_stat(). This is a prepare patch for
> the following memcg page stat lock simplifying.
> 
> Signed-off-by: Sha Zhengju <handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org>

Why we need to find page_cgroup and memcg and check pc->flags bit
even if memcg is unused ? I think it's too slow.

Sorry, NAK.



> ---
>   include/linux/memcontrol.h |   14 +++++++-------
>   mm/memcontrol.c            |    9 ++-------
>   mm/rmap.c                  |   28 +++++++++++++++++++++++++---
>   3 files changed, 34 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index d6183f0..7af3ed3 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -163,20 +163,20 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
>   	rcu_read_unlock();
>   }
>   
> -void mem_cgroup_update_page_stat(struct page *page,
> +void mem_cgroup_update_page_stat(struct mem_cgroup *memcg,
>   				 enum mem_cgroup_page_stat_item idx,
>   				 int val);
>   
> -static inline void mem_cgroup_inc_page_stat(struct page *page,
> +static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg,
>   					    enum mem_cgroup_page_stat_item idx)
>   {
> -	mem_cgroup_update_page_stat(page, idx, 1);
> +	mem_cgroup_update_page_stat(memcg, idx, 1);
>   }
>   
> -static inline void mem_cgroup_dec_page_stat(struct page *page,
> +static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg,
>   					    enum mem_cgroup_page_stat_item idx)
>   {
> -	mem_cgroup_update_page_stat(page, idx, -1);
> +	mem_cgroup_update_page_stat(memcg, idx, -1);
>   }
>   
>   unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
> @@ -347,12 +347,12 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
>   {
>   }
>   
> -static inline void mem_cgroup_inc_page_stat(struct page *page,
> +static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg,
>   					    enum mem_cgroup_page_stat_item idx)
>   {
>   }
>   
> -static inline void mem_cgroup_dec_page_stat(struct page *page,
> +static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg,
>   					    enum mem_cgroup_page_stat_item idx)
>   {
>   }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b31513e..a394ba4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2367,18 +2367,13 @@ void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
>   	move_unlock_mem_cgroup(pc->mem_cgroup, flags);
>   }
>   
> -void mem_cgroup_update_page_stat(struct page *page,
> +void mem_cgroup_update_page_stat(struct mem_cgroup *memcg,
>   				 enum mem_cgroup_page_stat_item idx, int val)
>   {
> -	struct mem_cgroup *memcg;
> -	struct page_cgroup *pc = lookup_page_cgroup(page);
> -	unsigned long uninitialized_var(flags);
> -
>   	if (mem_cgroup_disabled())
>   		return;
>   
> -	memcg = pc->mem_cgroup;
> -	if (unlikely(!memcg || !PageCgroupUsed(pc)))
> +	if (unlikely(!memcg))
>   		return;
>   
>   	switch (idx) {
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 6280da8..a03c2a9 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1109,12 +1109,24 @@ void page_add_file_rmap(struct page *page)
>   {
>   	bool locked;
>   	unsigned long flags;
> +	struct page_cgroup *pc;
> +	struct mem_cgroup *memcg = NULL;
>   
>   	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
> +	pc = lookup_page_cgroup(page);
> +
> +	rcu_read_lock();
> +	memcg = pc->mem_cgroup;
> +	if (unlikely(!PageCgroupUsed(pc)))
> +		memcg = NULL;
> +
>   	if (atomic_inc_and_test(&page->_mapcount)) {
>   		__inc_zone_page_state(page, NR_FILE_MAPPED);
> -		mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
> +		if (memcg)
> +			mem_cgroup_inc_page_stat(memcg, MEMCG_NR_FILE_MAPPED);
>   	}
> +	rcu_read_unlock();
> +
>   	mem_cgroup_end_update_page_stat(page, &locked, &flags);
>   }
>   
> @@ -1129,14 +1141,22 @@ void page_remove_rmap(struct page *page)
>   	bool anon = PageAnon(page);
>   	bool locked;
>   	unsigned long flags;
> +	struct page_cgroup *pc;
> +	struct mem_cgroup *memcg = NULL;
>   
>   	/*
>   	 * The anon case has no mem_cgroup page_stat to update; but may
>   	 * uncharge_page() below, where the lock ordering can deadlock if
>   	 * we hold the lock against page_stat move: so avoid it on anon.
>   	 */
> -	if (!anon)
> +	if (!anon) {
>   		mem_cgroup_begin_update_page_stat(page, &locked, &flags);
> +		pc = lookup_page_cgroup(page);
> +		rcu_read_lock();
> +		memcg = pc->mem_cgroup;
> +		if (unlikely(!PageCgroupUsed(pc)))
> +			memcg = NULL;
> +	}
>   
>   	/* page still mapped by someone else? */
>   	if (!atomic_add_negative(-1, &page->_mapcount))
> @@ -1157,7 +1177,9 @@ void page_remove_rmap(struct page *page)
>   					      NR_ANON_TRANSPARENT_HUGEPAGES);
>   	} else {
>   		__dec_zone_page_state(page, NR_FILE_MAPPED);
> -		mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
> +		if (memcg)
> +			mem_cgroup_dec_page_stat(memcg, MEMCG_NR_FILE_MAPPED);
> +		rcu_read_unlock();
>   		mem_cgroup_end_update_page_stat(page, &locked, &flags);
>   	}
>   	if (unlikely(PageMlocked(page)))
>