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page: maintain a lru list and do unloading from oldest to newest

--- a/sys/src/cmd/page.c

+++ b/sys/src/cmd/page.c

@@ -22,6 +22,9 @@

 	Page	*next;

 	Page	*down;

 	Page	*tail;

+

+	Page	*lnext;

+	Page	*lprev;

 };

 int zoom = 1;

@@ -32,6 +35,7 @@

 int viewgen;

 Point resize, pos;

 Page *root, *current;

+Page lru;

 QLock pagelock;

 int nullfd;

@@ -137,10 +141,6 @@

 	p->open = popen;

 	p->fd = fd;

-	p->down = nil;

-	p->tail = nil;

-	p->next = nil;

-

 	qlock(&pagelock);

 	if(p->up = up){

 		if(up->tail == nil)

@@ -829,11 +829,30 @@

 	return Dy(i->r)*bytesperline(i->r, i->depth);

 }

+static void

+lunlink(Page *p)

+{

+	if(p->lnext == nil || p->lnext == p)

+		return;

+	p->lnext->lprev = p->lprev;

+	p->lprev->lnext = p->lnext;

+	p->lnext = nil;

+	p->lprev = nil;

+}

+

 void

 loadpage(Page *p)

 {

 	int fd;

+	qlock(&lru);

+	lunlink(p);

+	p->lnext = lru.lnext;

+	p->lprev = &lru;

+	p->lnext->lprev = p;

+	p->lprev->lnext = p;

+	qunlock(&lru);

+

 	if(p->open && p->image == nil){

 		fd = openpage(p);

 		if(fd >= 0){

@@ -854,6 +873,10 @@

 void

 unloadpage(Page *p)

 {

+	qlock(&lru);

+	lunlink(p);

+	qunlock(&lru);

+

 	if(p->open == nil || p->image == nil)

 		return;

 	lockdisplay(display);

@@ -868,7 +891,7 @@

 {

 	Page *p;

-	for(p = root->down; p && imemsize >= limit; p = nextpage(p)){

+	while(imemsize >= limit && (p = lru.lprev) != &lru){

 		qlock(p);

 		unloadpage(p);

 		qunlock(p);

@@ -1500,6 +1523,8 @@

 	memset(&m, 0, sizeof(m));

 	if((nullfd = open("/dev/null", ORDWR)) < 0)

 		sysfatal("open: %r");

+	lru.lprev = &lru;

+	lru.lnext = &lru;

 	current = root = addpage(nil, "", nil, nil, -1);

 	if(*argv == nil && !imode)

 		addpage(root, "stdin", popenfile, strdup("/fd/0"), -1);

-- 

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