lib: make htable buffersize a template parameter

Previously you could name the number of pages you wanted htable to
allocate per BigBuf when calling the constructor. This can now be
selected as small/medium/large as a template parameter. As before the
default is large to provide best performance, but also produce maximum
overhead.

core/src/dird/ndmp_fhdb_mem.cc

@@ -111,7 +111,7 @@ struct ooo_metadata {
 };
 typedef struct ooo_metadata OOO_MD;
 
-using MetadataTable = htable<uint64_t, OOO_MD>;
+using MetadataTable = htable<uint64_t, OOO_MD, htableBufferSize::small>;
 
 struct fhdb_state_mem {
   N_TREE_ROOT* fhdb_root;
@@ -438,8 +438,7 @@ static inline void add_out_of_order_metadata(NIS* nis,
     item_size = sizeof(OOO_MD);
     nr_items = (nr_pages * B_PAGE_SIZE) / item_size;
 
-    meta_data
-        = new MetadataTable(md_entry, &md_entry->link, nr_items, nr_pages);
+    meta_data = new MetadataTable(md_entry, &md_entry->link, nr_items);
     ((struct fhdb_state_mem*)nis->fhdb_state)->out_of_order_metadata
         = meta_data;
   }

core/src/findlib/find.h

@@ -186,7 +186,7 @@ struct CurLink {
   char name[1];          /**< The name */
 };
 
-using LinkHash = htable<htable_binary_key, CurLink>;
+using LinkHash = htable<htable_binary_key, CurLink, htableBufferSize::medium>;
 
 
 /**

core/src/findlib/hardlink.cc

@@ -63,7 +63,7 @@ CurLink* new_hardlink(JobControlRecord* jcr,
   uint8_t* new_key;
 
   if (!ff_pkt->linkhash) {
-    ff_pkt->linkhash = new LinkHash(hl, &hl->link, 10000, 480);
+    ff_pkt->linkhash = new LinkHash(hl, &hl->link, 10000);
   }
 
   len = strlen(fname) + 1;

core/src/lib/htable.h

@@ -127,13 +127,32 @@ struct htable_binary_key {
   uint32_t len;
 };
 
-template <typename Key, typename T> class htable {
+enum class htableBufferSize
+{
+  small,
+  medium,
+  large
+};
+
+template <typename Key,
+          typename T,
+          enum htableBufferSize BufferSize = htableBufferSize::large>
+class htable {
   std::unique_ptr<htableImpl> pimpl;
 
  public:
   htable() { pimpl = std::make_unique<htableImpl>(); }
-  htable(T* item, hlink* link, int tsize = 31, int nr_pages = 0)
+  htable(T* item, hlink* link, int tsize = 31)
   {
+    int nr_pages = 0;
+    if constexpr (BufferSize == htableBufferSize::large) {
+      nr_pages = 0;
+    } else if constexpr (BufferSize == htableBufferSize::medium) {
+      nr_pages = 512;
+    } else if constexpr (BufferSize == htableBufferSize::small) {
+      nr_pages = 1;
+    }
+
     pimpl = std::make_unique<htableImpl>(item, link, tsize, nr_pages);
   }
   T* lookup(Key key)

core/src/lib/tree.cc

@@ -92,7 +92,7 @@ TREE_ROOT* new_tree(int count)
   root->type = TN_ROOT;
   root->fname = "";
   HL_ENTRY* entry = NULL;
-  new (&root->hardlinks) HardlinkTable(entry, &entry->link, 0, 1);
+  new (&root->hardlinks) HardlinkTable(entry, &entry->link);
   return root;
 }
 

core/src/lib/tree.h

@@ -108,7 +108,7 @@ struct s_hl_entry {
 };
 typedef struct s_hl_entry HL_ENTRY;
 
-using HardlinkTable = htable<uint64_t, HL_ENTRY>;
+using HardlinkTable = htable<uint64_t, HL_ENTRY, htableBufferSize::small>;
 
 struct s_tree_root {
   s_tree_root()