Re: [v5 PATCH 2/4] mm: move mem_cgroup_uncharge out of __page_cache_release()

[Kirill Tkhai]

On 07.08.2019 05:17, Yang Shi wrote:
> The later patch would make THP deferred split shrinker memcg aware, but
> it needs page->mem_cgroup information in THP destructor, which is called
> after mem_cgroup_uncharge() now.
> 
> So, move mem_cgroup_uncharge() from __page_cache_release() to compound
> page destructor, which is called by both THP and other compound pages
> except HugeTLB.  And call it in __put_single_page() for single order
> page.
> 
> Suggested-by: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Qian Cai <cai@xxxxxx>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>

Reviewed-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>

> ---
>  mm/page_alloc.c | 1 +
>  mm/swap.c       | 2 +-
>  mm/vmscan.c     | 6 ++----
>  3 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index df02a88..1d1c5d3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -670,6 +670,7 @@ static void bad_page(struct page *page, const char *reason,
>  
>  void free_compound_page(struct page *page)
>  {
> +	mem_cgroup_uncharge(page);
>  	__free_pages_ok(page, compound_order(page));
>  }
>  
> diff --git a/mm/swap.c b/mm/swap.c
> index ae30039..d4242c8 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -71,12 +71,12 @@ static void __page_cache_release(struct page *page)
>  		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>  	}
>  	__ClearPageWaiters(page);
> -	mem_cgroup_uncharge(page);
>  }
>  
>  static void __put_single_page(struct page *page)
>  {
>  	__page_cache_release(page);
> +	mem_cgroup_uncharge(page);
>  	free_unref_page(page);
>  }
>  
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index dbdc46a..b1b5e5f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1490,10 +1490,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		 * Is there need to periodically free_page_list? It would
>  		 * appear not as the counts should be low
>  		 */
> -		if (unlikely(PageTransHuge(page))) {
> -			mem_cgroup_uncharge(page);
> +		if (unlikely(PageTransHuge(page)))
>  			(*get_compound_page_dtor(page))(page);
> -		} else
> +		else
>  			list_add(&page->lru, &free_pages);
>  		continue;
>  
> @@ -1914,7 +1913,6 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>  
>  			if (unlikely(PageCompound(page))) {
>  				spin_unlock_irq(&pgdat->lru_lock);
> -				mem_cgroup_uncharge(page);
>  				(*get_compound_page_dtor(page))(page);
>  				spin_lock_irq(&pgdat->lru_lock);
>  			} else
>