[PATCH 2/3] jffs2: Add a "favourlzo" compression mode to jffs2

[Richard Purdie <rpurdie@openedhand.com>]

Add a "favourlzo" compression mode to jffs2 which tries to
optimise by size but gives lzo an advantage when comparing sizes.
This means the faster lzo algorithm can be preferred when there
isn't much difference in compressed size (the exact threshold can
be changed).

Signed-off-by: Richard Purdie <rpurdie@openedhand.com>
---
 fs/Kconfig       |    7 +++++++
 fs/jffs2/compr.c |   45 ++++++++++++++++++++++++++++++++++++++++-----
 fs/jffs2/compr.h |    3 +++
 3 files changed, 50 insertions(+), 5 deletions(-)

Index: linux/fs/Kconfig
===================================================================
--- linux.orig/fs/Kconfig	2007-07-10 10:15:53.000000000 +0100
+++ linux/fs/Kconfig	2007-07-10 10:16:04.000000000 +0100
@@ -1356,6 +1356,13 @@ config JFFS2_CMODE_SIZE
 	  Tries all compressors and chooses the one which has the smallest
 	  result.
 
+config JFFS2_CMODE_FAVOURLZO
+	bool "Favour LZO"
+	help
+	  Tries all compressors and chooses the one which has the smallest
+	  result but gives some preference to LZO (which has faster
+	  decompression) at the expense of size.
+
 endchoice
 
 config CRAMFS
Index: linux/fs/jffs2/compr.c
===================================================================
--- linux.orig/fs/jffs2/compr.c	2007-07-10 10:15:53.000000000 +0100
+++ linux/fs/jffs2/compr.c	2007-07-10 10:16:04.000000000 +0100
@@ -24,6 +24,34 @@ static int jffs2_compression_mode = JFFS
 /* Statistics for blocks stored without compression */
 static uint32_t none_stat_compr_blocks=0,none_stat_decompr_blocks=0,none_stat_compr_size=0;
 
+
+/*
+ * Return 1 to use this compression
+ */
+static int jffs2_is_best_compression(struct jffs2_compressor *this,
+		struct jffs2_compressor *best, uint32_t size, uint32_t bestsize)
+{
+	switch (jffs2_compression_mode) {
+	case JFFS2_COMPR_MODE_SIZE:
+		if (bestsize > size)
+			return 1;
+		return 0;
+	case JFFS2_COMPR_MODE_FAVOURLZO:
+		if ((this->compr == JFFS2_COMPR_LZO) && (bestsize > size))
+			return 1;
+		if ((best->compr != JFFS2_COMPR_LZO) && (bestsize > size))
+			return 1;
+		if ((this->compr == JFFS2_COMPR_LZO) && (bestsize > (size * FAVOUR_LZO_PERCENT / 100)))
+			return 1;
+		if ((bestsize * FAVOUR_LZO_PERCENT / 100) > size)
+			return 1;
+
+		return 0;
+	}
+	/* Shouldn't happen */
+	return 0;
+}
+
 /* jffs2_compress:
  * @data: Pointer to uncompressed data
  * @cdata: Pointer to returned pointer to buffer for compressed data
@@ -90,6 +118,7 @@ uint16_t jffs2_compress(struct jffs2_sb_
 			kfree(output_buf);
 		break;
 	case JFFS2_COMPR_MODE_SIZE:
+	case JFFS2_COMPR_MODE_FAVOURLZO:
 		orig_slen = *datalen;
 		orig_dlen = *cdatalen;
 		spin_lock(&jffs2_compressor_list_lock);
@@ -98,7 +127,7 @@ uint16_t jffs2_compress(struct jffs2_sb_
 			if ((!this->compress)||(this->disabled))
 				continue;
 			/* Allocating memory for output buffer if necessary */
-			if ((this->compr_buf_size<orig_dlen)&&(this->compr_buf)) {
+			if ((this->compr_buf_size < orig_slen) && (this->compr_buf)) {
 				spin_unlock(&jffs2_compressor_list_lock);
 				kfree(this->compr_buf);
 				spin_lock(&jffs2_compressor_list_lock);
@@ -107,15 +136,15 @@ uint16_t jffs2_compress(struct jffs2_sb_
 			}
 			if (!this->compr_buf) {
 				spin_unlock(&jffs2_compressor_list_lock);
-				tmp_buf = kmalloc(orig_dlen,GFP_KERNEL);
+				tmp_buf = kmalloc(orig_slen, GFP_KERNEL);
 				spin_lock(&jffs2_compressor_list_lock);
 				if (!tmp_buf) {
-					printk(KERN_WARNING "JFFS2: No memory for compressor allocation. (%d bytes)\n",orig_dlen);
+					printk(KERN_WARNING "JFFS2: No memory for compressor allocation. (%d bytes)\n", orig_slen);
 					continue;
 				}
 				else {
 					this->compr_buf = tmp_buf;
-					this->compr_buf_size = orig_dlen;
+					this->compr_buf_size = orig_slen;
 				}
 			}
 			this->usecount++;
@@ -126,7 +155,8 @@ uint16_t jffs2_compress(struct jffs2_sb_
 			spin_lock(&jffs2_compressor_list_lock);
 			this->usecount--;
 			if (!compr_ret) {
-				if ((!best_dlen)||(best_dlen>*cdatalen)) {
+				if (((!best_dlen) || jffs2_is_best_compression(this, best, *cdatalen, best_dlen))
+						&& (*cdatalen < *datalen)) {
 					best_dlen = *cdatalen;
 					best_slen = *datalen;
 					best = this;
@@ -298,9 +328,14 @@ int __init jffs2_compressors_init(void)
 	jffs2_compression_mode = JFFS2_COMPR_MODE_SIZE;
 	D1(printk(KERN_INFO "JFFS2: default compression mode: size\n");)
 #else
+#ifdef CONFIG_JFFS2_CMODE_FAVOURLZO
+	jffs2_compression_mode = JFFS2_COMPR_MODE_FAVOURLZO;
+	D1(printk(KERN_INFO "JFFS2: default compression mode: favourlzo\n");)
+#else
 	D1(printk(KERN_INFO "JFFS2: default compression mode: priority\n");)
 #endif
 #endif
+#endif
 	return 0;
 }
 
Index: linux/fs/jffs2/compr.h
===================================================================
--- linux.orig/fs/jffs2/compr.h	2007-07-10 10:15:53.000000000 +0100
+++ linux/fs/jffs2/compr.h	2007-07-10 10:16:04.000000000 +0100
@@ -38,6 +38,9 @@
 #define JFFS2_COMPR_MODE_NONE       0
 #define JFFS2_COMPR_MODE_PRIORITY   1
 #define JFFS2_COMPR_MODE_SIZE       2
+#define JFFS2_COMPR_MODE_FAVOURLZO  3
+
+#define FAVOUR_LZO_PERCENT 80
 
 struct jffs2_compressor {
 	struct list_head list;