bonefish+axeld:

* Removed the vm_cache/vm_store ref_count duality that besides being a bit ugly
  also created the page dameon cache retrieval problem: now, only areas (and
  cache consumers) retrieve a reference to the store (and therefore, the vnode).
  The page daemon doesn't need to care about this at all anymore, and the pseudo
  references of the vm_cache could be removed again.
* Rearranged deletion of vnodes such that its ID can be reused directly after
  fs_remove_vnode() has been called.
* vm_page_allocate_page() no longer panics when it runs out of pages, but just
  waits for new pages to become available using the new sFreeCondition condition
  variable - to make sure this happens in an acceptable time frame, it'll
  trigger a run of the low memory handlers.
* Implemented a page_thief() that steals inactive pages from caches and puts
  them into the free queue. It runs as a low memory handler.
* The file cache now sets the usage count on the pages it inserts into the
  cache (needs some rework though, cache_io() doesn't do it yet).
* Instead of panicking, the kernel will currently dead lock in low memory
  situations, since BFS does a bit too much in bfs_release_vnode().
* Some minor cleanup.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22315 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/cache/file_cache.cpp

@@ -612,6 +612,11 @@ read_chunk_into_cache(file_cache_ref *ref, off_t offset, size_t numBytes,
 	// make the pages accessible in the cache
 	for (int32 i = pageIndex; i-- > 0;) {
 		pages[i]->state = PAGE_STATE_ACTIVE;
+		if (pages[i]->usage_count < 0)
+			pages[i]->usage_count = 1;
+		else
+			pages[i]->usage_count++;
+
 		busyConditions[i].Unpublish();
 	}
 
@@ -792,6 +797,11 @@ write_chunk_to_cache(file_cache_ref *ref, off_t offset, size_t numBytes,
 	for (int32 i = pageIndex; i-- > 0;) {
 		busyConditions[i].Unpublish();
 
+		if (pages[i]->usage_count < 0)
+			pages[i]->usage_count = 1;
+		else
+			pages[i]->usage_count++;
+
 		if (writeThrough)
 			pages[i]->state = PAGE_STATE_ACTIVE;
 		else
@@ -1248,17 +1258,10 @@ file_cache_create(dev_t mountID, ino_t vnodeID, off_t size, int fd)
 	if (vfs_lookup_vnode(mountID, vnodeID, &ref->vnode) != B_OK)
 		goto err2;
 
-	// Gets (usually creates) the cache for the node - note, this does grab a
-	// reference to the node...
+	// Gets (usually creates) the cache for the node
 	if (vfs_get_vnode_cache(ref->vnode, &ref->cache, true) != B_OK)
 		goto err2;
 
-	// ... that we don't need, and therefore release it again.
-	// Our caller already holds a reference to the vnode; it will destroy us
-	// when the last one goes away (which, of course, can only ever happen if
-	// we don't grab an extra reference).
-	vfs_put_vnode(ref->vnode);
-
 	ref->cache->virtual_size = size;
 	((vnode_store *)ref->cache->store)->file_cache_ref = ref;
 	return ref;