- The backward prefetching method fails near start of file. Fix it.
- Make it scale up more quickly by adding ra_min to ra_size.
- Do not discount readahead_hit_rate, that's not a documented behavior.
Signed-off-by: Wu Fengguang <[email protected]>
---
--- linux-2.6.17-mm2.orig/mm/readahead.c
+++ linux-2.6.17-mm2/mm/readahead.c
@@ -1636,8 +1636,9 @@ initial_readahead(struct address_space *
* Important for certain scientific arenas(i.e. structural analysis).
*/
static int
-try_read_backward(struct file_ra_state *ra, pgoff_t begin_index,
- unsigned long ra_size, unsigned long ra_max)
+try_read_backward(struct file_ra_state *ra,
+ pgoff_t begin_index, unsigned long ra_size,
+ unsigned long ra_min, unsigned long ra_max)
{
pgoff_t end_index;
@@ -1646,11 +1647,11 @@ try_read_backward(struct file_ra_state *
return 0;
if ((ra->flags & RA_CLASS_MASK) == RA_CLASS_BACKWARD &&
- ra_has_index(ra, ra->prev_page)) {
- ra_size += 2 * ra->hit0;
+ ra_has_index(ra, ra->prev_page) && ra_cache_hit_ok(ra)) {
+ ra_size += ra_min + 2 * ra_readahead_size(ra);
end_index = ra->la_index;
} else {
- ra_size += ra_size + ra_size * (readahead_hit_rate - 1) / 2;
+ ra_size += ra_size * readahead_hit_rate;
end_index = ra->prev_page;
}
@@ -1661,7 +1662,7 @@ try_read_backward(struct file_ra_state *
if (end_index > begin_index + ra_size)
return 0;
- begin_index = end_index - ra_size;
+ begin_index = end_index > ra_size ? end_index - ra_size : 0;
ra_set_class(ra, RA_CLASS_BACKWARD);
ra_set_index(ra, begin_index, begin_index);
@@ -1864,7 +1865,7 @@ page_cache_readahead_adaptive(struct add
* Backward read-ahead.
*/
if (!page && begin_index == index &&
- try_read_backward(ra, index, size, ra_max))
+ try_read_backward(ra, index, size, ra_min, ra_max))
return ra_dispatch(ra, mapping, filp);
/*
--
-
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