Messages in this thread Patch in this message | | | Date | Fri, 26 May 2006 19:39:29 +0800 | From | Wu Fengguang <> | Subject | [PATCH 23/33] readahead: backward prefetching method |
| |
Readahead policy for reading backward.
Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn> ---
mm/readahead.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 files changed, 40 insertions(+)
--- linux-2.6.17-rc4-mm3.orig/mm/readahead.c +++ linux-2.6.17-rc4-mm3/mm/readahead.c @@ -1574,6 +1574,46 @@ initial_readahead(struct address_space * } /* + * Backward prefetching. + * + * No look-ahead and thrashing safety guard: should be unnecessary. + */ +static int +try_read_backward(struct file_ra_state *ra, pgoff_t begin_index, + unsigned long ra_size, unsigned long ra_max) +{ + pgoff_t end_index; + + /* Are we reading backward? */ + if (begin_index > ra->prev_page) + return 0; + + if ((ra->flags & RA_CLASS_MASK) == RA_CLASS_BACKWARD && + ra_has_index(ra, ra->prev_page)) { + ra_size += 2 * ra_cache_hit(ra, 0); + end_index = ra->la_index; + } else { + ra_size += ra_size + ra_size * (readahead_hit_rate - 1) / 2; + end_index = ra->prev_page; + } + + if (ra_size > ra_max) + ra_size = ra_max; + + /* Read traces close enough to be covered by the prefetching? */ + if (end_index > begin_index + ra_size) + return 0; + + begin_index = end_index - ra_size; + + ra_set_class(ra, RA_CLASS_BACKWARD); + ra_set_index(ra, begin_index, begin_index); + ra_set_size(ra, ra_size, 0); + + return 1; +} + +/* * ra_min is mainly determined by the size of cache memory. Reasonable? * * Table of concrete numbers for 4KB page size: -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |