1 files changed, 135 insertions, 2 deletions

diff --git a/builtin-gc.c b/builtin-gc.c
index 9397482610..956c32d1af 100644
--- a/builtin-gc.c
+++ b/builtin-gc.c
@@ -20,11 +20,13 @@ static const char builtin_gc_usage[] = "git-gc [--prune] [--aggressive]";
 
 static int pack_refs = 1;
 static int aggressive_window = -1;
+static int gc_auto_threshold = 6700;
+static int gc_auto_pack_limit = 20;
 
 #define MAX_ADD 10
 static const char *argv_pack_refs[] = {"pack-refs", "--all", "--prune", NULL};
 static const char *argv_reflog[] = {"reflog", "expire", "--all", NULL};
-static const char *argv_repack[MAX_ADD] = {"repack", "-a", "-d", "-l", NULL};
+static const char *argv_repack[MAX_ADD] = {"repack", "-d", "-l", NULL};
 static const char *argv_prune[] = {"prune", NULL};
 static const char *argv_rerere[] = {"rerere", "gc", NULL};
 
@@ -41,6 +43,14 @@ static int gc_config(const char *var, const char *value)
 		aggressive_window = git_config_int(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "gc.auto")) {
+		gc_auto_threshold = git_config_int(var, value);
+		return 0;
+	}
+	if (!strcmp(var, "gc.autopacklimit")) {
+		gc_auto_pack_limit = git_config_int(var, value);
+		return 0;
+	}
 	return git_default_config(var, value);
 }
 
@@ -57,10 +67,107 @@ static void append_option(const char **cmd, const char *opt, int max_length)
 	cmd[i] = NULL;
 }
 
+static int too_many_loose_objects(void)
+{
+	/*
+	 * Quickly check if a "gc" is needed, by estimating how
+	 * many loose objects there are.  Because SHA-1 is evenly
+	 * distributed, we can check only one and get a reasonable
+	 * estimate.
+	 */
+	char path[PATH_MAX];
+	const char *objdir = get_object_directory();
+	DIR *dir;
+	struct dirent *ent;
+	int auto_threshold;
+	int num_loose = 0;
+	int needed = 0;
+
+	if (gc_auto_threshold <= 0)
+		return 0;
+
+	if (sizeof(path) <= snprintf(path, sizeof(path), "%s/17", objdir)) {
+		warning("insanely long object directory %.*s", 50, objdir);
+		return 0;
+	}
+	dir = opendir(path);
+	if (!dir)
+		return 0;
+
+	auto_threshold = (gc_auto_threshold + 255) / 256;
+	while ((ent = readdir(dir)) != NULL) {
+		if (strspn(ent->d_name, "0123456789abcdef") != 38 ||
+		    ent->d_name[38] != '\0')
+			continue;
+		if (++num_loose > auto_threshold) {
+			needed = 1;
+			break;
+		}
+	}
+	closedir(dir);
+	return needed;
+}
+
+static int too_many_packs(void)
+{
+	struct packed_git *p;
+	int cnt;
+
+	if (gc_auto_pack_limit <= 0)
+		return 0;
+
+	prepare_packed_git();
+	for (cnt = 0, p = packed_git; p; p = p->next) {
+		char path[PATH_MAX];
+		size_t len;
+		int keep;
+
+		if (!p->pack_local)
+			continue;
+		len = strlen(p->pack_name);
+		if (PATH_MAX <= len + 1)
+			continue; /* oops, give up */
+		memcpy(path, p->pack_name, len-5);
+		memcpy(path + len - 5, ".keep", 6);
+		keep = access(p->pack_name, F_OK) && (errno == ENOENT);
+		if (keep)
+			continue;
+		/*
+		 * Perhaps check the size of the pack and count only
+		 * very small ones here?
+		 */
+		cnt++;
+	}
+	return gc_auto_pack_limit <= cnt;
+}
+
+static int need_to_gc(void)
+{
+	/*
+	 * Setting gc.auto and gc.autopacklimit to 0 or negative can
+	 * disable the automatic gc.
+	 */
+	if (gc_auto_threshold <= 0 && gc_auto_pack_limit <= 0)
+		return 0;
+
+	/*
+	 * If there are too many loose objects, but not too many
+	 * packs, we run "repack -d -l".  If there are too many packs,
+	 * we run "repack -A -d -l".  Otherwise we tell the caller
+	 * there is no need.
+	 */
+	if (too_many_packs())
+		append_option(argv_repack, "-A", MAX_ADD);
+	else if (!too_many_loose_objects())
+		return 0;
+	return 1;
+}
+
 int cmd_gc(int argc, const char **argv, const char *prefix)
 {
 	int i;
 	int prune = 0;
+	int auto_gc = 0;
 	char buf[80];
 
 	git_config(gc_config);
@@ -82,12 +189,34 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			}
 			continue;
 		}
-		/* perhaps other parameters later... */
+		if (!strcmp(arg, "--auto")) {
+			auto_gc = 1;
+			continue;
+		}
 		break;
 	}
 	if (i != argc)
 		usage(builtin_gc_usage);
 
+	if (auto_gc) {
+		/*
+		 * Auto-gc should be least intrusive as possible.
+		 */
+		prune = 0;
+		if (!need_to_gc())
+			return 0;
+	} else {
+		/*
+		 * Use safer (for shared repos) "-A" option to
+		 * repack when not pruning. Auto-gc makes its
+		 * own decision.
+		 */
+		if (prune)
+			append_option(argv_repack, "-a", MAX_ADD);
+		else
+			append_option(argv_repack, "-A", MAX_ADD);
+	}
+
 	if (pack_refs && run_command_v_opt(argv_pack_refs, RUN_GIT_CMD))
 		return error(FAILED_RUN, argv_pack_refs[0]);
 
@@ -103,5 +232,9 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	if (run_command_v_opt(argv_rerere, RUN_GIT_CMD))
 		return error(FAILED_RUN, argv_rerere[0]);
 
+	if (auto_gc && too_many_loose_objects())
+		warning("There are too many unreachable loose objects; "
+			"run 'git prune' to remove them.");
+
 	return 0;
 }