Improve zygote heap sharing.
Lots of ClassObject structures are unshared [and thus make whole pages
unshared]. A big contributor to this is the initializing class loader
logic, which has two writable words in a ClassObject and does indeed
seem to write them a lot.
Class which are created "early" have a low serial number and are
probably being created by the zygote, and would benefit from better
sharing. This change move the two words for classes with a low serial
number to a global, making the two words in those ClassObjects unused,
and thus more likely to be shared across apps.
Measured increase in sharing is c 100K per app, at a cost of c 32K
increase in unshared globals.
This might be better as a Set<Pair<Class,ClassLoader>> or
something. Many ClassObjects have zero loaders, and the typical count
seems to be very small. It should be possible to remove the two words
from the ClassObject and at the same time have a smaller global data
structure.
Respond to reviewer's comments.
Moved the "external" InitiatingLoaderList[] from gDvm to allocated storage.
Made the warning for the "const" go away.
Remove "vm/Init.c" from the commit
Revert Globals.h to not contain ZYGOTE_CLASS_CUTOFF
Use calloc rather than malloc/clear
diff --git a/vm/oo/Object.h b/vm/oo/Object.h
index 7ef8dac..18fbb36 100644
--- a/vm/oo/Object.h
+++ b/vm/oo/Object.h
@@ -24,6 +24,7 @@
/* fwd decl */
struct DataObject;
+struct InitiatingLoaderList;
struct ClassObject;
struct StringObject;
struct ArrayObject;
@@ -35,6 +36,7 @@
struct Field;
struct RegisterMap;
typedef struct DataObject DataObject;
+typedef struct InitiatingLoaderList InitiatingLoaderList;
typedef struct ClassObject ClassObject;
typedef struct StringObject StringObject;
typedef struct ArrayObject ArrayObject;
@@ -248,6 +250,18 @@
};
/*
+ * For classes created early and thus probably in the zygote, the
+ * InitiatingLoaderList is kept in gDvm. Later classes use the structure in
+ * Object Class. This helps keep zygote pages shared.
+ */
+struct InitiatingLoaderList {
+ /* a list of initiating loader Objects; grown and initialized on demand */
+ Object** initiatingLoaders;
+ /* count of loaders in the above list */
+ int initiatingLoaderCount;
+};
+
+/*
* Class objects have many additional fields. This is used for both
* classes and interfaces, including synthesized classes (arrays and
* primitive types).
@@ -318,8 +332,9 @@
Object* classLoader;
/* initiating class loader list */
- Object** initiatingLoaders;
- int initiatingLoaderCount;
+ /* NOTE: for classes with low serialNumber, these are unused, and the
+ values are kept in a table in gDvm. */
+ InitiatingLoaderList initiatingLoaderList;
/* array of interfaces this class implements directly */
int interfaceCount;