22 seconds -> 8.5 seconds running stat on /usr/src, 24 -> 5.6 seconds on a large Maildir

patch-stat.c.diff

Index: stat.c
===================================================================
--- stat.c	(revision 336221)
+++ stat.c	(working copy)
@@ -202,6 +202,30 @@
 		(*nl) = ((c) == '\n'); \
 	} while (0/*CONSTCOND*/)
 
+static struct passwd *
+cached_getpwuid(uid_t uid)
+{
+	static struct passwd *last = NULL;
+
+	if (!last || last->pw_uid != uid) {
+		last = getpwuid(uid);
+	}
+
+	return last;
+}
+
+static struct group *
+cached_getgrgid(gid_t gid)
+{
+	static struct group *last = NULL;
+
+	if (!last || last->gr_gid != gid) {
+		last = getgrgid(gid);
+	}
+
+	return last;
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -717,7 +741,7 @@
 	case SHOW_st_uid:
 		small = (sizeof(st->st_uid) == 4);
 		data = st->st_uid;
-		if ((pw = getpwuid(st->st_uid)) != NULL)
+		if ((pw = cached_getpwuid(st->st_uid)) != NULL)
 			sdata = pw->pw_name;
 		else {
 			snprintf(sid, sizeof(sid), "(%ld)", (long)st->st_uid);
@@ -731,7 +755,7 @@
 	case SHOW_st_gid:
 		small = (sizeof(st->st_gid) == 4);
 		data = st->st_gid;
-		if ((gr = getgrgid(st->st_gid)) != NULL)
+		if ((gr = cached_getgrgid(st->st_gid)) != NULL)
 			sdata = gr->gr_name;
 		else {
 			snprintf(sid, sizeof(sid), "(%ld)", (long)st->st_gid);