Let "git svn" run "git gc --auto" occasionally

Let "git svn" run "git gc --auto" every 1000 imported commits to
reduce the number of loose objects.

To handle the common use case of frequent imports, where each
invocation typically fetches much less than 1000 commits, also run gc
unconditionally at the end of the import.

"1000" is the same number that was used by default when we called
git-repack. It isn't necessarily still the best choice.

Signed-off-by: Karl Hasselström <kha@treskal.com>
Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-svn.perl

@@ -1247,6 +1247,8 @@ package Git::SVN;
 use File::Copy qw/copy/;
 use IPC::Open3;
 
+my ($_gc_nr, $_gc_period);
+
 # properties that we do not log:
 my %SKIP_PROP;
 BEGIN {
@@ -1407,6 +1409,7 @@ sub read_all_remotes {
 }
 
 sub init_vars {
+	$_gc_nr = $_gc_period = 1000;
 	if (defined $_repack || defined $_repack_flags) {
 	       warn "Repack options are obsolete; they have no effect.\n";
 	}
@@ -2095,6 +2098,10 @@ sub restore_commit_header_env {
 	}
 }
 
+sub gc {
+	command_noisy('gc', '--auto');
+};
+
 sub do_git_commit {
 	my ($self, $log_entry) = @_;
 	my $lr = $self->last_rev;
@@ -2148,6 +2155,10 @@ sub do_git_commit {
 		                   0, $self->svm_uuid);
 	}
 	print " = $commit ($self->{ref_id})\n";
+	if (--$_gc_nr == 0) {
+		$_gc_nr = $_gc_period;
+		gc();
+	}
 	return $commit;
 }
 
@@ -3975,6 +3986,7 @@ sub gs_fetch_loop_common {
 		$max += $inc;
 		$max = $head if ($max > $head);
 	}
+	Git::SVN::gc();
 }
 
 sub match_globs {