.

bigfile/_bigfile.c

@@ -414,6 +414,20 @@ PyFunc(pyfileh_invalidate_page, "invalidate_page(pgoffset) - invalidate fileh pa
 }
 
 
+PyFunc(pyfileh_uses_mmap_overlay, "uses_mmap_overlay() - whether base data for all VMAs"
+                                  " of this fileh are taken as base-layer mmap")
+    (PyObject *pyfileh0, PyObject *args)
+{
+    PyBigFileH  *pyfileh = container_of(pyfileh0, PyBigFileH, pyobj);
+    BigFileH    *fileh   = &pyfileh->fileh;
+
+    if (!PyArg_ParseTuple(args, ""))
+        return NULL;
+
+    return PyBool_FromLong(fileh->mmap_overlay);
+}
+
+
 static void
 pyfileh_dealloc(PyObject *pyfileh0)
 {
@@ -454,11 +468,12 @@ pyfileh_new(PyTypeObject *type, PyObject *args, PyObject *kw)
 
 
 static /*const*/ PyMethodDef pyfileh_methods[] = {
-    {"mmap",            pyfileh_mmap,           METH_VARARGS,   pyfileh_mmap_doc},
-    {"dirty_writeout",  pyfileh_dirty_writeout, METH_VARARGS,   pyfileh_dirty_writeout_doc},
-    {"dirty_discard",   pyfileh_dirty_discard,  METH_VARARGS,   pyfileh_dirty_discard_doc},
-    {"isdirty",         pyfileh_isdirty,        METH_VARARGS,   pyfileh_isdirty_doc},
-    {"invalidate_page", pyfileh_invalidate_page,METH_VARARGS,   pyfileh_invalidate_page_doc},
+    {"mmap",              pyfileh_mmap,              METH_VARARGS,  pyfileh_mmap_doc},
+    {"dirty_writeout",    pyfileh_dirty_writeout,    METH_VARARGS,  pyfileh_dirty_writeout_doc},
+    {"dirty_discard",     pyfileh_dirty_discard,     METH_VARARGS,  pyfileh_dirty_discard_doc},
+    {"isdirty",           pyfileh_isdirty,           METH_VARARGS,  pyfileh_isdirty_doc},
+    {"invalidate_page",   pyfileh_invalidate_page,   METH_VARARGS,  pyfileh_invalidate_page_doc},
+    {"uses_mmap_overlay", pyfileh_uses_mmap_overlay, METH_VARARGS,  pyfileh_uses_mmap_overlay_doc},
     {NULL}
 };
 

bigfile/file_zodb.py

@@ -781,6 +781,10 @@ class _ZBigFileH(object):
     def invalidate_page(self, pgoffset):
         return self.zfileh.invalidate_page(pgoffset)
 
+    @property
+    def uses_mmap_overlay(self):
+        return self.zfileh.uses_mmap_overlay
+
 
     # ~~~~ ISynchronizer ~~~~
     def beforeCompletion(self, txn):

bigfile/tests/test_filezodb.py

@@ -137,7 +137,10 @@ def test_bigfile_filezodb():
     # evict all loaded pages and test loading them again
     # (verifies ZBlk.loadblkdata() & loadblk logic when loading data the second time)
     reclaimed = ram_reclaim_all()
-    assert reclaimed >= blen    # XXX assumes pagesize=blksize
+    if fh.uses_mmap_overlay:
+        assert reclaimed == 0
+    else:
+        assert reclaimed >= blen    # XXX assumes pagesize=blksize
 
     for i in xrange(blen):
         assert array_equal(Blk(vma, i), dataX(i))