lz4hc compression in UBIFS?

[Brent Taylor]

On Fri, Sep 20, 2013 at 7:16 AM, Konstantin Tokarev <annulen at yandex.ru> wrote:
> Hi all,
>
> Are there any plans for adding lz4hc [1] compression support to UBIFS?
>
> Benchmarks are quite impressive, and it looks like lz4hc can achieve better compression ration while providing 3.5x faster decompression. From quick look at UBIFS module sources it looks like adding new compressor supported by crypto API is a matter of a few lines of code in compress.c.
>
> Or are there any known obstacles?
>
> [1] http://code.google.com/p/lz4/
>
> --
> Regards,
> Konstantin
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/

Here is a patch based on linux-3.12-rc3.  I haven't performed any
performance testing UBIFS using lz4hc, but I can mount UBIFS volumes
and haven't seen any problems yet.  The only think I know that isn't
correct about the patch is the description for the Kconfig element for
select lz4hc as a compression option.  I only copied the description
from the lzo description.

diff -uN -uNr linux-3.12-rc3.orig/fs/ubifs/compress.c
linux-3.12-rc3/fs/ubifs/compress.c
--- linux-3.12-rc3.orig/fs/ubifs/compress.c     2013-09-29
17:02:38.000000000 -0500
+++ linux-3.12-rc3/fs/ubifs/compress.c  2013-07-17 21:57:27.440653860 -0500
@@ -53,6 +53,22 @@
 };
 #endif

+#ifdef CONFIG_UBIFS_FS_LZ4HC
+static DEFINE_MUTEX(lz4hc_mutex);
+
+static struct ubifs_compressor lz4hc_compr = {
+       .compr_type = UBIFS_COMPR_LZ4HC,
+       .comp_mutex = &lz4hc_mutex,
+       .name = "lz4hc",
+       .capi_name = "lz4hc",
+};
+#else
+static struct ubifs_compressor lz4hc_compr = {
+       .compr_type = UBIFS_COMPR_LZ4HC,
+       .name = "lz4hc",
+};
+#endif
+
 #ifdef CONFIG_UBIFS_FS_ZLIB
 static DEFINE_MUTEX(deflate_mutex);
 static DEFINE_MUTEX(inflate_mutex);
@@ -224,10 +240,14 @@
 {
        int err;

-       err = compr_init(&lzo_compr);
+       err = compr_init(&lz4hc_compr);
        if (err)
                return err;

+       err = compr_init(&lzo_compr);
+       if (err)
+               goto out_lz4hc;
+
        err = compr_init(&zlib_compr);
        if (err)
                goto out_lzo;
@@ -237,6 +257,8 @@

 out_lzo:
        compr_exit(&lzo_compr);
+out_lz4hc:
+       compr_exit(&lz4hc_compr);
        return err;
 }

@@ -245,6 +267,7 @@
  */
 void ubifs_compressors_exit(void)
 {
+       compr_exit(&lz4hc_compr);
        compr_exit(&lzo_compr);
        compr_exit(&zlib_compr);
 }
diff -uN -uNr linux-3.12-rc3.orig/fs/ubifs/Kconfig
linux-3.12-rc3/fs/ubifs/Kconfig
--- linux-3.12-rc3.orig/fs/ubifs/Kconfig        2013-09-29
17:02:38.000000000 -0500
+++ linux-3.12-rc3/fs/ubifs/Kconfig     2013-10-03 21:40:39.098747630 -0500
@@ -29,6 +29,14 @@
           LZO compressor is generally faster than zlib but compresses worse.
           Say 'Y' if unsure.

+config UBIFS_FS_LZ4HC
+       bool "LZ4HC compression support" if UBIFS_FS_ADVANCED_COMPR
+       depends on UBIFS_FS && CRYPTO_LZ4HC
+       default y
+       help
+          LZ4HC compressor is generally faster than zlib but compresses worse.
+          Say 'Y' if unsure.
+
 config UBIFS_FS_ZLIB
        bool "ZLIB compression support" if UBIFS_FS_ADVANCED_COMPR
        depends on UBIFS_FS
diff -uN -uNr linux-3.12-rc3.orig/fs/ubifs/super.c
linux-3.12-rc3/fs/ubifs/super.c
--- linux-3.12-rc3.orig/fs/ubifs/super.c        2013-09-29
17:02:38.000000000 -0500
+++ linux-3.12-rc3/fs/ubifs/super.c     2013-09-30 23:01:06.899526709 -0500
@@ -1040,6 +1040,8 @@
                                return -ENOMEM;
                        if (!strcmp(name, "none"))
                                c->mount_opts.compr_type = UBIFS_COMPR_NONE;
+                       else if (!strcmp(name, "lz4hc"))
+                               c->mount_opts.compr_type = UBIFS_COMPR_LZ4HC;
                        else if (!strcmp(name, "lzo"))
                                c->mount_opts.compr_type = UBIFS_COMPR_LZO;
                        else if (!strcmp(name, "zlib"))
diff -uN -uNr linux-3.12-rc3.orig/fs/ubifs/ubifs-media.h
linux-3.12-rc3/fs/ubifs/ubifs-media.h
--- linux-3.12-rc3.orig/fs/ubifs/ubifs-media.h  2013-09-29
17:02:38.000000000 -0500
+++ linux-3.12-rc3/fs/ubifs/ubifs-media.h       2013-07-16
22:56:02.435523610 -0500
@@ -332,12 +332,14 @@
  * UBIFS_COMPR_NONE: no compression
  * UBIFS_COMPR_LZO: LZO compression
  * UBIFS_COMPR_ZLIB: ZLIB compression
+ * UBIFS_COMPR_LZ4HZ: LZ4HZ compression
  * UBIFS_COMPR_TYPES_CNT: count of supported compression types
  */
 enum {
        UBIFS_COMPR_NONE,
        UBIFS_COMPR_LZO,
        UBIFS_COMPR_ZLIB,
+       UBIFS_COMPR_LZ4HC,
        UBIFS_COMPR_TYPES_CNT,
 };

Enjoy,
Brent Taylor