linux-kernel - Re: [patch] mm: shmem: use new radix tree iterator

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Date:	Sun, 3 Feb 2013 18:01:53 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] mm: shmem: use new radix tree iterator

On Fri, 1 Feb 2013, Johannes Weiner wrote:

> In shmem_find_get_pages_and_swap, use the faster radix tree iterator
> construct from 78c1d78 "radix-tree: introduce bit-optimized iterator".
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Yes, that looks fine, and is testing out fine, thanks.
Acked-by: Hugh Dickins <hughd@...gle.com>

> ---
>  mm/shmem.c | 25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a368a1c..c5dc8ae 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -336,19 +336,19 @@ static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
>  					pgoff_t start, unsigned int nr_pages,
>  					struct page **pages, pgoff_t *indices)
>  {
> -	unsigned int i;
> -	unsigned int ret;
> -	unsigned int nr_found;
> +	void **slot;
> +	unsigned int ret = 0;
> +	struct radix_tree_iter iter;
> +
> +	if (!nr_pages)
> +		return 0;
>  
>  	rcu_read_lock();
>  restart:
> -	nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
> -				(void ***)pages, indices, start, nr_pages);
> -	ret = 0;
> -	for (i = 0; i < nr_found; i++) {
> +	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
>  		struct page *page;
>  repeat:
> -		page = radix_tree_deref_slot((void **)pages[i]);
> +		page = radix_tree_deref_slot(slot);
>  		if (unlikely(!page))
>  			continue;
>  		if (radix_tree_exception(page)) {
> @@ -365,17 +365,16 @@ static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
>  			goto repeat;
>  
>  		/* Has the page moved? */
> -		if (unlikely(page != *((void **)pages[i]))) {
> +		if (unlikely(page != *slot)) {
>  			page_cache_release(page);
>  			goto repeat;
>  		}
>  export:
> -		indices[ret] = indices[i];
> +		indices[ret] = iter.index;
>  		pages[ret] = page;
> -		ret++;
> +		if (++ret == nr_pages)
> +			break;
>  	}
> -	if (unlikely(!ret && nr_found))
> -		goto restart;
>  	rcu_read_unlock();
>  	return ret;
>  }
> -- 
> 1.7.11.7
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