linux-kernel - Re: [PATCH 2/3] mm, slub: count freed pages via rcu as this task's reclaimed

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Date:	Tue, 09 Apr 2013 17:38:28 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 2/3] mm, slub: count freed pages via rcu as this task's
 reclaimed_slab

Hi Joonsoo,
On 04/09/2013 09:21 AM, Joonsoo Kim wrote:
> Currently, freed pages via rcu is not counted for reclaimed_slab, because
> it is freed in rcu context, not current task context. But, this free is
> initiated by this task, so counting this into this task's reclaimed_slab
> is meaningful to decide whether we continue reclaim, or not.
> So change code to count these pages for this task's reclaimed_slab.
>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: Matt Mackall <mpm@...enic.com>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 4aec537..16fd2d5 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1409,8 +1409,6 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
>   
>   	memcg_release_pages(s, order);
>   	page_mapcount_reset(page);
> -	if (current->reclaim_state)
> -		current->reclaim_state->reclaimed_slab += pages;
>   	__free_memcg_kmem_pages(page, order);
>   }
>   
> @@ -1431,6 +1429,8 @@ static void rcu_free_slab(struct rcu_head *h)
>   
>   static void free_slab(struct kmem_cache *s, struct page *page)
>   {
> +	int pages = 1 << compound_order(page);

One question irrelevant this patch. Why slab cache can use compound 
page(hugetlbfs pages/thp pages)? They are just used by app to optimize 
tlb miss, is it?

> +
>   	if (unlikely(s->flags & SLAB_DESTROY_BY_RCU)) {
>   		struct rcu_head *head;
>   
> @@ -1450,6 +1450,9 @@ static void free_slab(struct kmem_cache *s, struct page *page)
>   		call_rcu(head, rcu_free_slab);
>   	} else
>   		__free_slab(s, page);
> +
> +	if (current->reclaim_state)
> +		current->reclaim_state->reclaimed_slab += pages;
>   }
>   
>   static void discard_slab(struct kmem_cache *s, struct page *page)

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