linux-kernel - Re: [PATCH 2/2] mm: __free_pages batch up 0-order pages for freeing

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Date:	Wed, 01 Apr 2015 14:48:13 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	linux-kernel@...r.kernel.org, mhocko@...e.cz,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	linux-mm@...ck.org (open list:MEMORY MANAGEMENT)
Subject: Re: [PATCH 2/2] mm: __free_pages batch up 0-order pages for freeing

On Wed, Apr 01 2015, Sasha Levin <sasha.levin@...cle.com> wrote:

> Rather than calling free_hot_cold_page() for every page, batch them up in a
> list and pass them on to free_hot_cold_page_list(). This will let us defer
> them to a workqueue.
>
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> ---
>  mm/page_alloc.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 812ca75..e58e795 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2997,12 +2997,16 @@ EXPORT_SYMBOL(get_zeroed_page);
>  
>  void __free_pages(struct page *page, unsigned int order)
>  {
> +	LIST_HEAD(hot_cold_pages);
> +
>  	if (put_page_testzero(page)) {
>  		if (order == 0)
> -			free_hot_cold_page(page, false);
> +			list_add(&page->lru, &hot_cold_pages);
>  		else
>  			__free_pages_ok(page, order);
>  	}
> +
> +	free_hot_cold_page_list(&hot_cold_pages, false);

Is there a reason to do this function call when the list is empty? In
other words, why can't this just be done inside the if (order == 0)?

Rasmus
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