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

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Message-Id: <20090412102952.0dd377d6.akpm@linux-foundation.org>
Date:	Sun, 12 Apr 2009 10:29:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Vladislav Bolkhovitin <vst@...b.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] radix-tree: add radix_tree_prev_hole()

On Sun, 12 Apr 2009 15:19:51 +0800 Wu Fengguang <fengguang.wu@...el.com> wrote:

> +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;
> +}

argh.  This is about as inefficient as we could possibly make it :(

Really, this function should dive into radix-tree internals and walk
individual radix_tree_node.slots[] arrays.  And heck, it can peek at
radix_tree_node.count and _bypass_ entire nodes, too.

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