| Date | Fri, 26 May 2006 10:27:16 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 17/33] readahead: context based method |
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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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