[PATCH 15/16] readahead: reduce MMAP_LOTSAMISS for mmap read-around

From: Wu Fengguang
Date: Mon Mar 01 2010 - 00:40:01 EST

Now that we lifts readahead size from 128KB to 512KB,
the MMAP_LOTSAMISS shall be shrinked accordingly.

We shrink it a bit more, so that for sparse random access patterns,
only 10*512KB or ~5MB memory will be wasted, instead of the previous
100*128KB or ~12MB. The new threshold "10" is still big enough to avoid
turning off read-around for typical executable/lib page faults.

CC: Nick Piggin <npiggin@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
mm/filemap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- linux.orig/mm/filemap.c 2010-02-21 23:56:22.000000000 +0800
+++ linux/mm/filemap.c 2010-02-21 23:56:26.000000000 +0800
@@ -1393,7 +1393,7 @@ static int page_cache_read(struct file *
return ret;

-#define MMAP_LOTSAMISS (100)
+#define MMAP_LOTSAMISS (10)

* Synchronous readahead happens when we don't even find

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