linux-kernel - Re: [PATCH 1/3] radix-tree: add radix_tree_next

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Date:	Fri, 10 Apr 2009 21:29:03 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vladislav Bolkhovitin <vst@...b.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] radix-tree: add radix_tree_next_hole()

Heh silly mistake: the title should say radix_tree_prev_hole()
and the changelog should be 'counterpart of radix_tree_next_hole()'.

Will resubmit this one...

On Fri, Apr 10, 2009 at 09:12:48PM +0800, Wu, Fengguang wrote:
> The counterpart of radix_tree_prev_hole(). To be used by context readahead.
> 
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
> ---
>  include/linux/radix-tree.h |    2 +
>  lib/radix-tree.c           |   37 +++++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> --- mm.orig/lib/radix-tree.c
> +++ mm/lib/radix-tree.c
> @@ -666,6 +666,43 @@ unsigned long radix_tree_next_hole(struc
>  }
>  EXPORT_SYMBOL(radix_tree_next_hole);
>  
> +/**
> + *	radix_tree_prev_hole    -    find the prev hole (not-present entry)
> + *	@root:		tree root
> + *	@index:		index key
> + *	@max_scan:	maximum range to search
> + *
> + *	Search backwards in the range [max(index-max_scan+1, 0), index]
> + *	for the first hole.
> + *
> + *	Returns: the index of the hole if found, otherwise returns an index
> + *	outside of the set specified (in which case 'index - return >= max_scan'
> + *	will be true). In rare cases of wrap-around, LONG_MAX will be returned.
> + *
> + *	radix_tree_next_hole may be called under rcu_read_lock. However, like
> + *	radix_tree_gang_lookup, this will not atomically search a snapshot of
> + *	the tree at a single point in time. For example, if a hole is created
> + *	at index 10, then subsequently a hole is created at index 5,
> + *	radix_tree_prev_hole covering both indexes may return 5 if called under
> + *	rcu_read_lock.
> + */
> +unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
> +				   unsigned long index, unsigned long max_scan)
> +{
> +	unsigned long i;
> +
> +	for (i = 0; i < max_scan; i++) {
> +		if (!radix_tree_lookup(root, index))
> +			break;
> +		index--;
> +		if (index == LONG_MAX)
> +			break;
> +	}
> +
> +	return index;
> +}
> +EXPORT_SYMBOL(radix_tree_prev_hole);
> +
>  static unsigned int
>  __lookup(struct radix_tree_node *slot, void ***results, unsigned long index,
>  	unsigned int max_items, unsigned long *next_index)
> --- mm.orig/include/linux/radix-tree.h
> +++ mm/include/linux/radix-tree.h
> @@ -167,6 +167,8 @@ radix_tree_gang_lookup_slot(struct radix
>  			unsigned long first_index, unsigned int max_items);
>  unsigned long radix_tree_next_hole(struct radix_tree_root *root,
>  				unsigned long index, unsigned long max_scan);
> +unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
> +				unsigned long index, unsigned long max_scan);
>  int radix_tree_preload(gfp_t gfp_mask);
>  void radix_tree_init(void);
>  void *radix_tree_tag_set(struct radix_tree_root *root,
> 
> -- 
--
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