clean up paging code.
- eliminate onswap() because it is not supported
(that leaves pagedout() looking kind of funny, doesn't it?)
- eliminate funny pagechainhead/pageunchainhead in newpage.
it was hard to follow, and resulted in funny looking code.
- nil not 0

Reference: /n/atom/patch/applied/pageclean
Date: Mon Jun  9 23:53:53 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/port/segment.c	Mon Jun  9 23:50:46 2014
+++ /sys/src/nix/port/segment.c	Mon Jun  9 23:50:46 2014
@@ -316,18 +316,11 @@
 			 * We construct a list of the pages to be freed, zero
 			 * the entries, then (below) call procflushseg, and call
 			 * putpage on the whole list.
-			 *
-			 * Swapped-out pages don't appear in TLBs, so it's okay
-			 * to putswap those pages before procflushseg.
 			 */
 			if(pg){
-				if(onswap(pg))
-					putswap(pg);
-				else{
-					pg->next = list;
-					list = pg;
-				}
-				s->map[i]->pages[j] = 0;
+				pg->next = list;
+				list = pg;
+				s->map[i]->pages[j] = nil;
 			}
 			if(--pages == 0)
 				goto out;
--- /sys/src/nix/port/page.c	Mon Jun  9 23:50:46 2014
+++ /sys/src/nix/port/page.c	Mon Jun  9 23:50:46 2014
@@ -83,7 +83,6 @@
 	for(si = 0; si < m->npgsz; si++)
 		if(size == m->pgsz[si])
 			return si;
-	print("getpgszi: size %#ulx not found\n", size);
 	return -1;
 }
 
@@ -94,13 +93,16 @@
 	int si;
 
 	si = getpgszi(size);
+	if(si == -1){
+		print("pgalloc: getpgszi %lux %d %#p\n", size, color, getcallerpc(&size));
+		return nil;
+	}
 	if((pg = malloc(sizeof(Page))) == nil){
 		DBG("pgalloc: malloc failed\n");
 		return nil;
 	}
-	memset(pg, 0, sizeof *pg);
 	if((pg->pa = physalloc(size, &color, pg)) == 0){
-		DBG("pgalloc: physalloc failed: size %#ulx color %d\n", size, color);
+		DBG("pgalloc: physalloc failed: size %#lux color %d\n", size, color);
 		free(pg);
 		return nil;
 	}
@@ -173,10 +175,10 @@
 	}
 	else {
 		pa->tail = p;
-		p->next = 0;
+		p->next = nil;
 	}
 	pa->head = p;
-	p->prev = 0;
+	p->prev = nil;
 	pa->freecount++;
 }
 
@@ -198,7 +200,6 @@
 {
 	Page *p;
 	KMap *k;
-	uchar ct;
 	Pgsza *pa;
 	int i, dontalloc, si;
 	static int once;
@@ -220,17 +221,17 @@
 		 * 1. try to reuse a free one.
 		 */
 		p = findpg(pa->head, color);
-		if(p != nil)
+		if(p != nil){
+			pageunchain(p);
 			break;
+		}
 
 		/*
 		 * 2. try to allocate a new one from physical memory
 		 */
 		p = pgalloc(size, color);
-		if(p != nil){
-			pagechainhead(p);
+		if(p != nil)
 			break;
-		}
 
 		/*
 		 * 3. out of memory, try with the pager.
@@ -239,16 +240,12 @@
 		unlock(&pga);
 
 		dontalloc = 0;
-		if(s && *s) {
+		if(s != nil && *s != nil) {
 			qunlock(&((*s)->lk));
-			*s = 0;
+			*s = nil;
 			dontalloc = 1;
 		}
 
-		/*
-		 * Try to get any page of the desired color
-		 * or any color for NOCOLOR.
-		 */
 		kickpager(si, color);
 
 		/*
@@ -263,11 +260,6 @@
 		lock(&pga);
 	}
 
-	assert(p != nil);
-	ct = PG_NEWCOL;
-
-	pageunchain(p);
-
 	lock(p);
 	if(p->ref != 0)
 		panic("newpage pa %#P", p->pa);
@@ -277,7 +269,7 @@
 	p->va = va;
 	p->modref = 0;
 	for(i = 0; i < nelem(p->cachectl); i++)
-		p->cachectl[i] = ct;
+		p->cachectl[i] = PG_NEWCOL;
 	unlock(p);
 	unlock(&pga);
 
@@ -611,14 +603,10 @@
 	dst = &new->pages[old->first-old->pages];
 	new->first = dst;
 	for(src = old->first; src <= old->last; src++, dst++)
-		if(*src){
-			if(onswap(*src))
-				panic("ptecpy: no swap");
-			else{
-				lock(*src);
-				(*src)->ref++;
-				unlock(*src);
-			}
+		if(*src != nil){
+			lock(*src);
+			(*src)->ref++;
+			unlock(*src);
 			new->last = dst;
 			*dst = *src;
 		}
@@ -659,7 +647,7 @@
 		}
 		for(pg = p->pages; pg < ptop; pg++) {
 			pt = *pg;
-			if(pt == 0)
+			if(pt == nil)
 				continue;
 			lock(pt);
 			ref = --pt->ref;
--- /sys/src/nix/port/portdat.h	Mon Jun  9 23:50:46 2014
+++ /sys/src/nix/port/portdat.h	Mon Jun  9 23:50:46 2014
@@ -429,10 +429,7 @@
 	SG_CEXEC	= 0100,		/* Detach at exec */
 };
 
-#define PG_ONSWAP	1
-#define onswap(s)	(PTR2UINT(s) & PG_ONSWAP)
-#define pagedout(s)	(PTR2UINT(s) == 0 || onswap(s))
-#define swapaddr(s)	(PTR2UINT(s) & ~PG_ONSWAP)
+#define pagedout(s)	(s == nil)
 
 #define SEGMAXPG	(SEGMAPSIZE)