kernel: make image cache not hold onto the channel, remove nocache flag

the image cache should not hold onto the text file channel
when not neccesary. now, the image keeps track of the number
of page cache references in Image.pgref. if the number of
page cache references and Image.ref are equal, this means
all the references to this image are from the page cache.
so no segments are using this image. in that case, we can
close the channel, but keep the Image in the hash table.

when attachimage() finds our image, it will check if Image.c
is nil and reattach the channel to the image before it is
used.

the Image.nocache flag isnt needed anymore.

1 files changed, 15 insertions, 8 deletions

diff --git a/sys/src/9/port/page.c b/sys/src/9/port/page.c
index 50cb4efca..f9eda93f7 100644
--- a/sys/src/9/port/page.c
+++ b/sys/src/9/port/page.c
@@ -228,9 +228,6 @@ putpage(Page *p)
 		return;
 	}
 
-	if(p->image && p->image->nocache)
-		uncachepage(p);
-
 	if(p->image && p->image != &swapimage)
 		pagechaintail(p);
 	else 
@@ -294,8 +291,8 @@ duppage(Page *p)				/* Always call with p locked */
 		return;
 	}
 
-	/* No freelist cache with uncached image or when memory is very low */
-	if(p->image->nocache || palloc.freecount < swapalloc.highwater) {
+	/* No freelist cache when memory is very low */
+	if(palloc.freecount < swapalloc.highwater) {
 		unlock(&palloc);
 		uncachepage(p);
 		return;
@@ -360,8 +357,10 @@ void
 uncachepage(Page *p)			/* Always called with a locked page */
 {
 	Page **l, *f;
+	Image *i;
 
-	if(p->image == 0)
+	i = p->image;
+	if(i == 0)
 		return;
 
 	lock(&palloc.hashlock);
@@ -374,9 +373,13 @@ uncachepage(Page *p)			/* Always called with a locked page */
 		l = &f->hash;
 	}
 	unlock(&palloc.hashlock);
-	putimage(p->image);
 	p->image = 0;
 	p->daddr = 0;
+
+	lock(i);
+	i->pgref--;
+	unlock(i);
+	putimage(i);
 }
 
 void
@@ -392,7 +395,11 @@ cachepage(Page *p, Image *i)
 	if(p->image)
 		panic("cachepage");
 
-	incref(i);
+	lock(i);
+	i->ref++;
+	i->pgref++;
+	unlock(i);
+
 	lock(&palloc.hashlock);
 	p->image = i;
 	l = &pghash(p->daddr);