* get_vnode() did not decrease the sUnusedVnodes counter when taking one node

of that list.
* Added a vfs_free_unused_vnodes() function that calls the low memory handler
  directly.
* create_sem_etc() now calls the above function in case there are no semaphores
  available anymore; this usually frees up to 2 semaphores per node (one from
  the cache if there is a file cache attached, and eventually one from the
  file system).


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@16610 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/vfs.h

@@ -96,6 +96,7 @@ status_t vfs_get_fs_node_from_path(mount_id mountID, const char *path,
 status_t vfs_stat_vnode(void *_vnode, struct stat *stat);
 status_t vfs_get_vnode_name(void *vnode, char *name, size_t nameSize);
 status_t vfs_get_cwd(mount_id *_mountID, vnode_id *_vnodeID);
+void vfs_free_unused_vnodes(int32 level);
 
 /* special module convenience call */
 status_t vfs_get_module_path(const char *basePath, const char *moduleName,

src/system/kernel/fs/vfs.cpp

@@ -816,6 +816,7 @@ restart:
 		if (vnode->ref_count == 0) {
 			// this vnode has been unused before
 			list_remove_item(&sUnusedVnodeList, vnode);
+			sUnusedVnodes--;
 		}
 		inc_vnode_ref_count(vnode);
 	} else {
@@ -2816,6 +2817,13 @@ vfs_get_cwd(mount_id *_mountID, vnode_id *_vnodeID)
 }
 
 
+extern "C" void
+vfs_free_unused_vnodes(int32 level)
+{
+	vnode_low_memory_handler(NULL, level);
+}
+
+
 extern "C" bool
 vfs_can_page(void *_vnode, void *cookie)
 {

src/system/kernel/sem.c

@@ -21,6 +21,8 @@
 #include <debug.h>
 #include <thread.h>
 #include <team.h>
+#include <vfs.h>
+#include <vm_low_memory.h>
 #include <vm_page.h>
 #include <boot/kernel_args.h>
 
@@ -257,7 +259,21 @@ create_sem_etc(int32 count, const char *name, team_id owner)
 	char *tempName;
 	size_t nameLength;
 
-	if (sSemsActive == false || sUsedSems == sMaxSems)
+	if (sSemsActive == false)
+		return B_NO_MORE_SEMS;
+
+	if (sUsedSems == sMaxSems) {
+		// The vnode cache may have collected lots of semaphores.
+		// Freeing some unused vnodes should improve our situation.
+		// TODO: maybe create a generic "low resources" handler, instead
+		//	of only the specialised low memory thing?
+		vfs_free_unused_vnodes(B_LOW_MEMORY_WARNING);
+	}
+	if (sUsedSems == sMaxSems) {
+		// try again with more enthusiasm
+		vfs_free_unused_vnodes(B_LOW_MEMORY_CRITICAL);
+	}
+	if (sUsedSems == sMaxSems)
 		return B_NO_MORE_SEMS;
 
 	if (name == NULL)