Inform about bitmap sizes and improve documentation

src/buddy_storage.c

@@ -718,6 +718,8 @@ sbu_mapper(size_t *sz, void *priv)
 
 	CAST_OBJ_NOTNULL(stv, priv, STEVEDORE_MAGIC);
 
+	fprintf(stderr, "buddy: metadata (bitmap) memory: %zu bytes\n",
+	    *sz);
 	return (VSMW_Allocf(heritage.proc_vsmw, NULL,
 	    VSM_CLASS_SLASH, *sz, "buddy.%s", stv->vclname));
 }

src/fellow_storage.c

@@ -1038,6 +1038,8 @@ sfe_mapper(size_t *sz, void *priv)
 
 	CAST_OBJ_NOTNULL(stv, priv, STEVEDORE_MAGIC);
 
+	fprintf(stderr, "fellow: metadata (bitmap) memory: %zu bytes\n",
+	    *sz);
 	return (VSMW_Allocf(heritage.proc_vsmw, NULL,
 		VSM_CLASS_SLASH, *sz, "fellow.%s", stv->vclname));
 }

src/vmod_slash.vcc

@@ -251,9 +251,11 @@ memory overhead.
 The *size* argument will be rounded down to a multiple of the
 (possibly rounded) *minpage* argument.
 
-In addition to the configured memory, approximately 1 / ( *minpage* *
-8) bytes are required for metadata (bitmaps). For the default
-*minpage* of 64 Bytes, this amounts to approximately 0.2%.
+Besides the configured memory size, approximately 1 / ( *minpage* *
+4) of it is additionally required for metadata (bitmaps) in the
+varnish home directory and in memory. For the default *minpage* of 64
+Bytes, this amounts to approximately 0.4%. The actual figure is output
+at startup as ``buddy: metadata (bitmap) size``.
 
 This storage can *not* be used via ``storage.``\ *<name>*.
 
@@ -394,6 +396,13 @@ On Linux, the memory cache will be allocated from huge pages, if
 available and if *memsize* is larger than a huge page. *memsize* will
 then be rounded up to a multiple of the respective huge page size.
 
+Besides the configured memory cache size, approximately 1 / 256 (0.4%)
+of *memsize* plus 1 / 16384 (0.006%) of *dsksize* will be required in
+the varnish home directory and in memory. For example, for
+``dsksize=1t`` and ``memsize=1g``, this amounts to roughly 70MB. The
+actual figures are output at startup as ``fellow: metadata (bitmap)
+memory``.
+
 *objsize_hint* (default 256KB) is used to sanity check *memsize* in
 relation to *dsksize*. It should be set to a value lower than the
 average object size (actual or expected). If *memsize* is configured