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authorArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2008-10-26 16:58:25 +0200
committerArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2008-12-03 13:13:50 +0200
commit062e4fee4400f283307cf8ac1b7931c939010229 (patch)
treecacea4a2f65688ad02fa572060155783c4f0377c /fs/ubifs
parentf6f7b52e2f6149d2ee365717afff315b05720162 (diff)
downloadop-kernel-dev-062e4fee4400f283307cf8ac1b7931c939010229.zip
op-kernel-dev-062e4fee4400f283307cf8ac1b7931c939010229.tar.gz
UBIFS: slight compression optimization
If data does not compress, it is better to leave it uncompressed because we'll read it faster then. So do not compress data if we save less than 64 bytes. Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Diffstat (limited to 'fs/ubifs')
-rw-r--r--fs/ubifs/compress.c6
-rw-r--r--fs/ubifs/ubifs-media.h7
2 files changed, 10 insertions, 3 deletions
diff --git a/fs/ubifs/compress.c b/fs/ubifs/compress.c
index a0ada59..6414d50 100644
--- a/fs/ubifs/compress.c
+++ b/fs/ubifs/compress.c
@@ -119,10 +119,10 @@ void ubifs_compress(const void *in_buf, int in_len, void *out_buf, int *out_len,
}
/*
- * Presently, we just require that compression results in less data,
- * rather than any defined minimum compression ratio or amount.
+ * If the data compressed only slightly, it is better to leave it
+ * uncompressed to improve read speed.
*/
- if (ALIGN(*out_len, 8) >= ALIGN(in_len, 8))
+ if (in_len - *out_len < UBIFS_MIN_COMPRESS_DIFF)
goto no_compr;
return;
diff --git a/fs/ubifs/ubifs-media.h b/fs/ubifs/ubifs-media.h
index 0b37804..b25fc36 100644
--- a/fs/ubifs/ubifs-media.h
+++ b/fs/ubifs/ubifs-media.h
@@ -51,6 +51,13 @@
*/
#define UBIFS_MIN_COMPR_LEN 128
+/*
+ * If compressed data length is less than %UBIFS_MIN_COMPRESS_DIFF bytes
+ * shorter than uncompressed data length, UBIFS preferes to leave this data
+ * node uncompress, because it'll be read faster.
+ */
+#define UBIFS_MIN_COMPRESS_DIFF 64
+
/* Root inode number */
#define UBIFS_ROOT_INO 1
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