(copy of message sent to the rdist developers)

X-url: http://www.isi.edu/~johnh/
To: rdist-dev
Subject: rdist memory consumption problem (with fix)
Date: Thu, 04 Feb 1999 14:59:30 -0800
From: John Heidemann <johnh.edu>


I've found a serious memory consumption problem for rdist
when running
over directories that contain many hard-linked files.  The
attached
patch fixes this problem at the cost of ~12 more lines of
code and a
little more dynamic memory allocation.

Rdist allocates a fixed-sized buffer (struct linkbuf in
defs.h) for
each file that has more than one hard link.  This buffer
includes
pre-allocated space for 3 strings, each of length BUFSIZ.
Undef
Redhat 5.2/linux-2.0.36 BUFSIZ is 8KB, so a lot of this
buffer goes to
waste.

For my mh mailbox directory (mh---even worse than news
spools at
stressing file systems!), I have ~54k directory entires,
~35k files
with only one link and ~8300 with 2-7 links.  With typical
rdist this
was resulting memory usage of >90MB and much swapping on my
poor
laptop.  With the included fix memory for this case is <3MB.

A remaining problem is that rdist does a linear search for
links in
its list, but this is a second-order problem to swapping.
(If I were
to fix the linear-search problem I'd probably grab the Tcl
implementation of resizing hashes since it's debuged and
reasonabally
small.  Would you be willing to accept that kind of a fix
for linear
searchs?)

The attached patch is against the redhat-5.2 (a slightly
patched)
version of rdist-6.1.0.  I looked at the source for
dist-6.1.5; the
code I change looked the same to me.

(Thanks for keeping rdist open source so users can find and
fix these
kinds of problems!)

   -John Heidemann
    USC/ISI

----------------------------------------

--- ./src/client.c-	Mon Jun  5 07:49:38 1995
+++ ./src/client.c	Thu Feb  4 13:46:51 1999
@@ -301,6 +301,18 @@
 	return(0);
 }

+void freelinkinfo(lp)
+	struct linkbuf *lp;
+{
+	if (lp->pathname)
+		free(lp->pathname);
+	if (lp->src)
+		free(lp->src);
+	if (lp->target)
+		free(lp->target);
+	free(lp);
+}
+
 /*
  * Save and retrieve hard link info
  */
@@ -309,6 +321,7 @@
 {
 	struct linkbuf *lp;

+	/* xxx: linear search doesn't scale with many links */
 	for (lp = ihead; lp != NULL; lp = lp->nextp)
 		if (lp->inum == statp->st_ino && lp->devnum ==
statp->st_dev) {
 			lp->count--;
@@ -321,12 +334,14 @@
 	lp->inum = statp->st_ino;
 	lp->devnum = statp->st_dev;
 	lp->count = statp->st_nlink - 1;
-	(void) strcpy(lp->pathname, target);
-	(void) strcpy(lp->src, source);
+	lp->pathname = strdup(target);
+	lp->src = strdup(source);
 	if (Tdest)
-		(void) strcpy(lp->target, Tdest);
+		lp->target = strdup(Tdest);
 	else
-		*lp->target = CNULL;
+		lp->target = NULL;
+	if (!lp->pathname || !lp->src || !(Tdest && lp->target))
+		fatalerr("Cannot malloc memory in linkinfo.");

 	return((struct linkbuf *) NULL);
 }
--- ./src/docmd.c-	Tue Apr 26 10:10:09 1994
+++ ./src/docmd.c	Thu Feb  4 13:46:33 1999
@@ -568,7 +568,7 @@
 	if (!nflag) {
 		register struct linkbuf *nextl, *l;

-		for (l = ihead; l != NULL; free((char *)l), l = nextl) {
+		for (l = ihead; l != NULL; freelinkinfo(l), l = nextl) {
 			nextl = l->nextp;
 			if (contimedout || IS_ON(opts, DO_IGNLNKS) ||
 			    l->count == 0)
--- ./include/defs.h-	Mon Apr 11 16:19:22 1994
+++ ./include/defs.h	Thu Feb  4 13:36:54 1999
@@ -300,9 +300,9 @@
 	ino_t	inum;
 	dev_t	devnum;
 	int	count;
-	char	pathname[BUFSIZ];
-	char	src[BUFSIZ];
-	char	target[BUFSIZ];
+	char	*pathname;
+	char	*src;
+	char	*target;
 	struct	linkbuf *nextp;
 };