Re: [PATCH 17/33] readahead: context based method

[Andrew Morton <akpm@osdl.org>]

Wu Fengguang <wfg@mail.ustc.edu.cn> wrote:
>
> This is the slow code path of adaptive read-ahead.
> 
> ...
>
> +
> +/*
> + * Count/estimate cache hits in range [first_index, last_index].
> + * The estimation is simple and optimistic.
> + */
> +static int count_cache_hit(struct address_space *mapping,
> +				pgoff_t first_index, pgoff_t last_index)
> +{
> +	struct page *page;
> +	int size = last_index - first_index + 1;

`size' might overflow.

> +	int count = 0;
> +	int i;
> +
> +	cond_resched();
> +	read_lock_irq(&mapping->tree_lock);
> +
> +	/*
> +	 * The first page may well is chunk head and has been accessed,
> +	 * so it is index 0 that makes the estimation optimistic. This
> +	 * behavior guarantees a readahead when (size < ra_max) and
> +	 * (readahead_hit_rate >= 16).
> +	 */
> +	for (i = 0; i < 16;) {
> +		page = __find_page(mapping, first_index +
> +						size * ((i++ * 29) & 15) / 16);

29?


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