remove dupseg.

Reference: /n/atom/patch/applied/nodupseg
Date: Thu Jun 12 02:27:05 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/port/page.c	Thu Jun 12 02:26:41 2014
+++ /sys/src/nix/port/page.c	Thu Jun 12 02:26:43 2014
@@ -252,7 +252,7 @@
 		 * reacquired the segment locks
 		 */
 		if(dontalloc)
-			return 0;
+			return nil;
 
 		lock(&pga);
 	}
@@ -352,98 +352,6 @@
 	unlock(&pga);
 
 	return p;
-}
-
-static int dupretries = 15000;
-
-int
-duppage(Page *p)				/* Always call with p locked */
-{
-	Pgsza *pa;
-	Page *np;
-	int color;
-	int retries;
-
-	retries = 0;
-retry:
-
-	if(retries++ > dupretries){
-		print("duppage %d, up %#p\n", retries, up);
-		dupretries += 100;
-		if(dupretries > 100000)
-			panic("duppage");
-		uncachepage(p);
-		return 1;
-	}
-
-	/* don't dup pages with no image */
-	if(p->ref == 0 || p->image == nil || p->image->notext)
-		return 0;
-
-	/*
-	 *  normal lock ordering is to call
-	 *  lock(&pga) before lock(p).
-	 *  To avoid deadlock, we have to drop
-	 *  our locks and try again.
-	 */
-	if(!canlock(&pga)){
-		unlock(p);
-		if(up)
-			sched();
-		lock(p);
-		goto retry;
-	}
-
-	pa = &pga.pgsza[p->pgszi];
-	/* No freelist cache when memory is very low */
-	if(pa->freecount < Nminfree){
-		unlock(&pga);
-		uncachepage(p);
-		return 1;
-	}
-
-	color = p->color;
-	for(np = pa->head; np; np = np->next)
-		if(np->color == color)
-			break;
-
-	/* No page of the correct color */
-	if(np == nil){
-		unlock(&pga);
-		uncachepage(p);
-		return 1;
-	}
-
-	pageunchain(np);
-	pagechaintail(np);
-	/*
-	 * XXX - here's a bug? - np is on the freelist but it's not really free.
-	 * when we unlock palloc someone else can come in, decide to
-	 * use np, and then try to lock it.  they succeed after we've
-	 * run copypage and cachepage and unlock(np).  then what?
-	 * they call pageunchain before locking(np), so it's removed
-	 * from the freelist, but still in the cache because of
-	 * cachepage below.  if someone else looks in the cache
-	 * before they remove it, the page will have a nonzero ref
-	 * once they finally lock(np).
-	 *
-	 * What I know is that not doing the pagechaintail, but
-	 * doing it at the end, to prevent the race, leads to a
-	 * deadlock, even following the pga, pg lock ordering. -nemo
-	 */
-	lock(np);
-	unlock(&pga);
-
-	/* Cache the new version */
-	uncachepage(np);
-	np->va = p->va;
-	np->daddr = p->daddr;
-	copypage(p, np);
-	cachepage(np, p->image);
-	unlock(np);
-	uncachepage(p);
-
-	return 0;
 }
 
 void
--- /sys/src/nix/port/fault.c	Thu Jun 12 02:26:45 2014
+++ /sys/src/nix/port/fault.c	Thu Jun 12 02:26:46 2014
@@ -148,23 +148,19 @@
 		lock(lkp);
 
 		ref = lkp->ref;
-		if(ref > 1) {
+		if(ref == 0)
+			panic("mach%d: %s %d fault %#p ref == 0", m->machno, up->text, up->pid, lkp);
+		if(ref == 1 && lkp->image == nil)
+			unlock(lkp);
+		else{
 			unlock(lkp);
-
 			new = newpage(0, &s, addr, pgsz, color);
-			if(s == 0)
+			if(s == nil)
 				return -1;
 			*pg = new;
 			copypage(lkp, *pg);
 			putpage(lkp);
 		}
-		else {
-			/* save a copy of the original for the image cache */
-			if(lkp->image != nil)
-				duppage(lkp);
-
-			unlock(lkp);
-		}
 		mmuattr = PTEWRITE|PTEVALID;
 		(*pg)->modref = PG_MOD|PG_REF;
 		break;
@@ -225,8 +221,8 @@
 			*p = new;
 			return;
 		}
-//iprint("pio: (%s) %#.4ux %#P %#lux	pgsz=%#P\n", chanpath(s->image->c), s->type, addr, soff, pgsz);
 		c = s->image->c;
+//iprint("pio: (%s) %#.4ux %#P %#lux	pgsz=%#P\n", chanpath(c), s->type, addr, soff, pgsz);
 		ask = s->flen-soff;
 
 		if(ask < 0){
--- /sys/src/nix/port/portfns.h	Thu Jun 12 02:26:49 2014
+++ /sys/src/nix/port/portfns.h	Thu Jun 12 02:26:50 2014
@@ -83,7 +83,6 @@
 void		dumpregs(Ureg*);
 void		dumpstack(void);
 Fgrp*		dupfgrp(Fgrp*);
-int		duppage(Page*);
 Segment*	dupseg(Segment**, int, int);
 void		dupswap(Page*);
 char*		edfadmit(Proc*);