Re: [PATCH] Make zlib compression level configurable, and change default.

[Joachim B Haga <cjhaga@fys.uio.no>]

Linus Torvalds <torvalds@osdl.org> writes:

> [snip suggested improvements]

Yes, that would be more... thorough. And, especially for the

  int zlib_compression_level = Z_DEFAULT_COMPRESSION;

line, more self-explanatory, too. So here's an updated patch
(replacing the previous) including your suggestions.

-j.

-

Make zlib compression level configurable, and change default.

With the change in default, "git add ." on kernel dir is about
twice as fast as before, with only minimal (0.5%) change in
object size. The speed difference is even more noticeable
when committing large files, which is now up to 8 times faster.

The configurability is through setting core.compression = [-1..9]
which maps to the zlib constants; -1 is the default, 0 is no
compression, and 1..9 are various speed/size tradeoffs, 9
being slowest.

Signed-off-by: Joachim B Haga (cjhaga@fys.uio.no)
---
 Documentation/config.txt |    6 ++++++
 cache.h                  |    1 +
 config.c                 |   10 ++++++++++
 environment.c            |    1 +
 sha1_file.c              |    4 ++--
 5 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index a04c5ad..ac89be7 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -91,6 +91,12 @@ core.warnAmbiguousRefs::
        If true, git will warn you if the ref name you passed it is ambiguous
        and might match multiple refs in the .git/refs/ tree. True by default.
 
+core.compression:
+       An integer -1..9, indicating the compression level for objects that
+       are not in a pack file. -1 is the zlib and git default. 0 means no 
+       compression, and 1..9 are various speed/size tradeoffs, 9 being
+       slowest.
+
 alias.*::
        Command aliases for the gitlink:git[1] command wrapper - e.g.
        after defining "alias.last = cat-file commit HEAD", the invocation
diff --git a/cache.h b/cache.h
index 8719939..84770bf 100644
--- a/cache.h
+++ b/cache.h
@@ -183,6 +183,7 @@ extern int log_all_ref_updates;
 extern int warn_ambiguous_refs;
 extern int shared_repository;
 extern const char *apply_default_whitespace;
+extern int zlib_compression_level;
 
 #define GIT_REPO_VERSION 0
 extern int repository_format_version;
diff --git a/config.c b/config.c
index ec44827..b23f4bf 100644
--- a/config.c
+++ b/config.c
@@ -279,6 +279,16 @@ int git_default_config(const char *var, 
                return 0;
        }
 
+       if (!strcmp(var, "core.compression")) {
+               int level = git_config_int(var, value);
+               if (level == -1)
+                       level = Z_DEFAULT_COMPRESSION;
+               else if (level < 0 || level > Z_BEST_COMPRESSION)
+                       die("bad zlib compression level %d", level);
+               zlib_compression_level = level;
+               return 0;
+       }
+
        if (!strcmp(var, "user.name")) {
                strlcpy(git_default_name, value, sizeof(git_default_name));
                return 0;
diff --git a/environment.c b/environment.c
index 3de8eb3..43823ff 100644
--- a/environment.c
+++ b/environment.c
@@ -20,6 +20,7 @@ int repository_format_version = 0;
 char git_commit_encoding[MAX_ENCODING_LENGTH] = "utf-8";
 int shared_repository = PERM_UMASK;
 const char *apply_default_whitespace = NULL;
+int zlib_compression_level = Z_DEFAULT_COMPRESSION;
 
 static char *git_dir, *git_object_dir, *git_index_file, *git_refs_dir,
        *git_graft_file;
diff --git a/sha1_file.c b/sha1_file.c
index 8179630..bc35808 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1458,7 +1458,7 @@ int write_sha1_file(void *buf, unsigned 
 
        /* Set it up */
        memset(&stream, 0, sizeof(stream));
-       deflateInit(&stream, Z_BEST_COMPRESSION);
+       deflateInit(&stream, zlib_compression_level);
        size = deflateBound(&stream, len+hdrlen);
        compressed = xmalloc(size);
 
@@ -1511,7 +1511,7 @@ static void *repack_object(const unsigne
 
        /* Set it up */
        memset(&stream, 0, sizeof(stream));
-       deflateInit(&stream, Z_BEST_COMPRESSION);
+       deflateInit(&stream, zlib_compression_level);
        size = deflateBound(&stream, len + hdrlen);
        buf = xmalloc(size);
 
-- 
1.4.1.g8fced-dirty