put a limit (default 1MB) on the read buffer size. This stops it

growing too much if the sender is much faster than the receiver

io.c

@@ -75,6 +75,9 @@ static void read_check(int f)
 	/* things could deteriorate if we read in really small chunks */
 	if (n < 10) n = 1024;
 
+	if (n > MAX_READ_BUFFER/4)
+		n = MAX_READ_BUFFER/4;
+
 	if (read_buffer_p != read_buffer) {
 		memmove(read_buffer,read_buffer_p,read_buffer_len);
 		read_buffer_p = read_buffer;
@@ -334,6 +337,7 @@ static int writefd_unbuffered(int fd,char *buf,int len)
 
 
     if (ret == -1) {
+	    if (read_buffer_len < MAX_READ_BUFFER)
 		    read_check(buffer_f_in);
 
 	    fd_count = fd+1;
@@ -350,6 +354,7 @@ static int writefd_unbuffered(int fd,char *buf,int len)
 	    tv.tv_usec = 0;
 	    count = select(fd_count,buffer_f_in == -1? NULL: &r_fds,
 			   &w_fds,NULL,&tv);
+
 	    if (count == -1 && errno != EINTR) {
 		    if (verbose > 1) 
 			    rprintf(FERROR,"select error: %s\n", strerror(errno));

rsync.h

@@ -52,6 +52,7 @@
 #define CHUNK_SIZE (32*1024)
 #define MAX_MAP_SIZE (4*1024*1024)
 #define IO_BUFFER_SIZE (4096)
+#define MAX_READ_BUFFER (1024*1024)
 
 #define MAX_ARGS 1000