[patch 1/2] readahead sysctl parameters fix

[Fengguang Wu]

- do no extra readahead when (readahead_ratio == 1)
- define readahead_hit_rate inside CONFIG_ADAPTIVE_READAHEAD ifdefs

Signed-off-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
---

--- linux-2.6.19-rc6-mm1.orig/include/linux/mm.h
+++ linux-2.6.19-rc6-mm1/include/linux/mm.h
@@ -1074,7 +1074,7 @@ extern int readahead_ratio;
 
 static inline int prefer_adaptive_readahead(void)
 {
-	return readahead_ratio > 1;
+	return readahead_ratio != 1;
 }
 
 /* Do stack extension */
--- linux-2.6.19-rc6-mm1.orig/Documentation/sysctl/vm.txt
+++ linux-2.6.19-rc6-mm1/Documentation/sysctl/vm.txt
@@ -234,7 +234,7 @@ plenty of memory(>>2MB per reader), a bi
 readahead_ratio also selects the readahead logic:
 	VALUE	CODE PATH
 	-------------------------------------------
-	    0	disable readahead totally
+	    0	read as is, no extra readahead
 	    1	select the stock readahead logic
 	2-100	select the adaptive readahead logic
 
--- linux-2.6.19-rc6-mm1.orig/mm/readahead.c
+++ linux-2.6.19-rc6-mm1/mm/readahead.c
@@ -40,10 +40,10 @@
 /* Set read-ahead size to ##% of the thrashing-threshold. */
 int readahead_ratio = 50;
 EXPORT_SYMBOL_GPL(readahead_ratio);
-#endif
 
 /* Readahead as long as cache hit ratio keeps above 1/##. */
 int readahead_hit_rate = 0;
+#endif /* CONFIG_ADAPTIVE_READAHEAD */
 
 /*
  * Detailed classification of read-ahead behaviors.

--
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