f2fs: reduce batch size of fstrim

This is to reduce the batch size of fstrim to avoid long latency.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index f478cb6..59eed3e 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -158,7 +158,7 @@
 	CP_DISCARD,
 };
 
-#define DEF_BATCHED_TRIM_SECTIONS	32
+#define DEF_BATCHED_TRIM_SECTIONS	2
 #define BATCHED_TRIM_SEGMENTS(sbi)	\
 		(SM_I(sbi)->trim_sections * (sbi)->segs_per_sec)
 #define BATCHED_TRIM_BLOCKS(sbi)	\