[9front] page(1) performance fixes

[qwx@sciops.net]

Hello,

The following patch attempts to improve page(1) performance, a huge
annoyance of mine, especially when files are themselves slow to load.
My benchmark is a t61p where these issues are extremely noticeable.

- fix showpage1 only decrementing proc counter once limit is reached;
this blocked having more than one loadpages process after NPROC calls,
since the next one has to wait until the last has exited, which is why
page(1) always hangs around after every few pages (if memory limit is
large enough anyway, but even with the default)
- allow procs to skip pages currently being loaded by others; this
forced processes to wait for each other when reaching the same page,
which happens all of the time
- (hack) immediately fork NPROC times after adding all pages at
startup to force loading a batch of pages in parallel

Thoughts?  If it's all good, I'd like to commit this.

Thanks,
qwx


diff 6e64d30454f71ecda88dba1bd792e97509115d73 uncommitted
--- a//sys/src/cmd/page.c
+++ b//sys/src/cmd/page.c
@@ -951,7 +951,8 @@
 loadpages(Page *p, int oviewgen)
 {
 	while(p != nil && viewgen == oviewgen){
-		qlock(p);
+		if(!canqlock(p))
+			goto next;
 		loadpage(p);
 		if(viewgen != oviewgen){
 			unloadpage(p);
@@ -974,6 +975,7 @@
 		qunlock(p);
 		if(p != current && imemsize >= imemlimit)
 			break;		/* only one page ahead once we reach the limit */
+	next:
 		if(forward < 0){
 			if(p->up == nil || p->up->down == p)
 				break;
@@ -1309,16 +1311,17 @@
 	writeaddr(p, "/dev/label");
 	current = p;
 	oviewgen = viewgen;
+	if(nproc >= NPROC)
+		waitpid();
 	switch(rfork(RFPROC|RFMEM)){
 	case -1:
 		sysfatal("rfork: %r");
 	case 0:
 		loadpages(p, oviewgen);
+		nproc--;
 		exits(nil);
 	}
-	if(++nproc >= NPROC)
-		if(waitpid() > 0)
-			nproc--;
+	nproc++;
 }
 
 /* recursive display lock, called from main proc only */
@@ -1691,6 +1694,8 @@
 		addpage(root, "stdin", popenfile, strdup("/fd/0"), -1);
 	for(; *argv; argv++)
 		addpage(root, *argv, popenfile, strdup(*argv), -1);
+	for(i=0; i<NPROC; i++)		/* rice */
+		showpage(current);
 
 	drawlock(1);
 	for(;;){