Removed the condition that only caches with a source can be merged.

Instead we only allow temporary caches to be merged. This remedies the
problem that after fork() + join() there remains a superfluous cache
layer for all RAM areas.
I haven't tested it, but this might improve the jam situation
memory-wise (huge heap is committed one less time), though it might
worsen it performance-wise (lots of heap pages are moved with every
merge).


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25717 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/vm/vm_cache.cpp

@@ -383,7 +383,7 @@ delete_cache(vm_cache* cache)
 static bool
 is_cache_mergeable(vm_cache* cache)
 {
-	return (cache->areas == NULL && cache->source != NULL
+	return (cache->areas == NULL && cache->temporary
 		&& !list_is_empty(&cache->consumers)
 		&& cache->consumers.link.next == cache->consumers.link.prev);
 }
@@ -488,9 +488,10 @@ merge_cache_with_only_consumer(vm_cache* cache)
 		}
 	}
 
+	// The remaining consumer has got a new source.
+	if (cache->source != NULL) {
 		vm_cache* newSource = cache->source;
 
-	// The remaining consumer has got a new source
 		mutex_lock(&newSource->lock);
 
 		list_remove_item(&newSource->consumers, cache);
@@ -499,9 +500,11 @@ merge_cache_with_only_consumer(vm_cache* cache)
 		cache->source = NULL;
 
 		mutex_unlock(&newSource->lock);
+	} else
+		consumer->source = NULL;
 
 	// Release the reference the cache's consumer owned. The consumer takes
-	// over the cache's ref to its source instead.
+	// over the cache's ref to its source (if any) instead.
 if (cache->ref_count < 2)
 panic("cacheRef %p ref count too low!\n", cache);
 	vm_cache_release_ref(cache);