[PATCH 7/8] readahead: call scheme: fix thrashed unaligned read

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

[-- Attachment #1: readahead-call-scheme-fix-thrashed-unaligned-read.patch --]
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When doing unaligned/subpages sequential reads, and thrashing happened,
it is possible that (offset == prev_page),
besides the normal  (offset == prev_page + 1).

We do not have such problem for the state based method.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/readahead.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- linux-2.6.20-rc4-mm1.orig/mm/readahead.c
+++ linux-2.6.20-rc4-mm1/mm/readahead.c
@@ -1618,7 +1618,7 @@ page_cache_readahead_adaptive(struct add
 	/*
 	 * Recover from possible thrashing.
 	 */
-	if (!page && offset == ra->prev_page + 1 && ra_has_index(ra, offset))
+	if (!page && offset - ra->prev_page <= 1 && ra_has_index(ra, offset))
 		return thrashing_recovery_readahead(mapping, filp, ra,
 								offset, ra_max);
 

--