The context method will lead to noticable overhead on sparse random reads.
Having the readahead window to start slowly makes it much better.
Signed-off-by: Wu Fengguang <[email protected]>
---
--- linux-2.6.17-mm2.orig/mm/readahead.c
+++ linux-2.6.17-mm2/mm/readahead.c
@@ -1548,6 +1548,11 @@ try_context_based_readahead(struct addre
return -1;
} else if (prev_page || probe_page(mapping, index - 1)) {
ra_index = index;
+ /*
+ * Slow start of readahead window.
+ * It helps avoid most readahead miss on sparse random reads.
+ */
+ ra_min = readahead_hit_rate;
} else if (readahead_hit_rate > 1) {
ra_index = find_segtail_backward(mapping, index,
readahead_hit_rate + ra_min);
--
-
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