Basic support for dedupe

This adds and option, dedupe_percentage, that controls how many of
the write IO buffers are identical. For instance, if this is set:

dedupe_percentage=70

then 70% of the write IO buffers will have identical contents. The
specific contents are, as before, controlled by the various options
that set buffer contents or buffer compressibility.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/thread_options.h b/thread_options.h
index e545a8f..a45d7b7 100644
--- a/thread_options.h
+++ b/thread_options.h
@@ -184,6 +184,7 @@
 	unsigned int buffer_pattern_bytes;
 	unsigned int compress_percentage;
 	unsigned int compress_chunk;
+	unsigned int dedupe_percentage;
 	unsigned int time_based;
 	unsigned int disable_lat;
 	unsigned int disable_clat;
@@ -403,8 +404,9 @@
 	uint32_t scramble_buffers;
 	uint8_t buffer_pattern[MAX_PATTERN_SIZE];
 	uint32_t buffer_pattern_bytes;
-	unsigned int compress_percentage;
-	unsigned int compress_chunk;
+	uint32_t compress_percentage;
+	uint32_t compress_chunk;
+	uint32_t dedupe_percentage;
 	uint32_t time_based;
 	uint32_t disable_lat;
 	uint32_t disable_clat;