[JFFS2] Add a "favourlzo" compression mode

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>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --git a/fs/Kconfig b/fs/Kconfig
index a2ec0b375dff34ca29d5581699876f2ad2c1772a..42cfb7dc95b5d8d48e25a07bf6d2b5d342e8a953 100644 (file)
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -1364,6 +1364,13 @@ 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

diff --git a/fs/jffs2/compr.c b/fs/jffs2/compr.c
index bcc28d266a122380bf66fd3484d47ccad53d4d03..86739ee53b37336c15cbc341180c47d195d9081a 100644 (file)
--- a/fs/jffs2/compr.c
+++ b/fs/jffs2/compr.c
@@ -24,6 +24,34 @@ static int jffs2_compression_mode = JFFS2_COMPR_MODE_PRIORITY;
 /* 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_info *c, struct jffs2_inode_info *f,
                        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_info *c, struct jffs2_inode_info *f,
                        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_info *c, struct jffs2_inode_info *f,
                        }
                        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_info *c, struct jffs2_inode_info *f,
                        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;
@@ -297,9 +327,14 @@ int __init jffs2_compressors_init(void)
 #ifdef CONFIG_JFFS2_CMODE_SIZE
        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;
 }

diff --git a/fs/jffs2/compr.h b/fs/jffs2/compr.h
index a54828a4e9c6cafff75f455c6f843fd1a1e0e609..e1b7efb70aa4951322f60582df08ce6687f1f6a6 100644 (file)
--- a/fs/jffs2/compr.h
+++ b/fs/jffs2/compr.h
@@ -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;