[PATCH 07/14] readahead: call scheme: catch thrashing on lookahead time

[Fengguang Wu]

Move the call to thrashing_recovery_readahead() before state_based_readahead().

That catches the rare case where thrashing happened on the time we are to read
the page at ra->lookahead_index. Obviously this case should be handled by
thrashing_recovery_readahead() instead of state_based_readahead().

Signed-off-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
---
 mm/readahead.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- linux-2.6.21-rc3-mm2.orig/mm/readahead.c
+++ linux-2.6.21-rc3-mm2/mm/readahead.c
@@ -1638,6 +1638,13 @@ page_cache_readahead_adaptive(struct add
 		return initial_readahead(mapping, filp, ra, req_size);
 
 	/*
+	 * Recover from possible thrashing.
+	 */
+	if (!page && offset - ra->prev_page <= 1 && ra_has_index(ra, offset))
+		return thrashing_recovery_readahead(mapping, filp, ra,
+								offset, ra_max);
+
+	/*
 	 * State based sequential read-ahead.
 	 */
 	if (offset == ra->prev_page + 1 &&
@@ -1647,13 +1654,6 @@ page_cache_readahead_adaptive(struct add
 						offset, req_size, ra_max);
 
 	/*
-	 * Recover from possible thrashing.
-	 */
-	if (!page && offset - ra->prev_page <= 1 && ra_has_index(ra, offset))
-		return thrashing_recovery_readahead(mapping, filp, ra,
-								offset, ra_max);
-
-	/*
 	 * Backward read-ahead.
 	 */
 	if (!page && try_backward_prefetching(ra, offset, req_size, ra_max))

--
-
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