Hi Ioi,
Here is the updated webrev with the warning message below for the
Integer cache.
http://cr.openjdk.java.net/~jiangli/8212995/webrev.03/
995 *
996 * WARNING: The cache is archived with CDS and reloaded from
the shared
997 * archive at runtime. The archived cache (Integer[]) and
Integer objects
998 * reside in the closed archive heap regions. Care should be
taken when
999 * changing the implementation and the cache array should not
be assigned
1000 * with new Integer object(s) after initialization.
Including core-lib-dev mailing list since the change now touches the
core library file.
Thanks,
Jiangli
On 11/1/18 10:58 PM, Jiangli Zhou wrote:
Hi Ioi,
On Nov 1, 2018, at 9:37 PM, Ioi Lam <ioi....@oracle.com> wrote:
Hi Jiangli,
576 void HeapShared::check_closed_archive_heap_region_object(InstanceKlass* k,
577 Thread* THREAD) {
578 // Check fields in the object
579 for (JavaFieldStream fs(k); !fs.done(); fs.next()) {
580 if (!fs.access_flags().is_static()) {
581 BasicType ft = fs.field_descriptor().field_type();
582 if (!fs.access_flags().is_final() && (ft == T_ARRAY || T_OBJECT)) {
583 ResourceMark rm(THREAD);
584 log_warning(cds, heap)(
585 "Please check reference field in %s instance in closed archive heap
region: %s %s",
586 k->external_name(), (fs.name())->as_C_string(),
587 (fs.signature())->as_C_string());
588 }
589 }
590 }
591 }
Checking that all static fields of the affected class (IntegerCache in this
case) are final is not enough. The elements of a final array can be modified.
Just to clarify, the above checks all instance fields (non-static fields) in
non-array objects. Static fields are not checked as mirrors are not in the
closed archive heap region. In the IntegerCache subgraph case, it makes sure
there is no non-final reference instance field in cached Integer objects (for
future proof).
JLS requires that
https://docs.oracle.com/javase/specs/jls/se8/html/jls-5.html#jls-5.1.7
If the value p being boxed is an integer literal of type int between -128 and
127 inclusive (§3.10.1), or the boolean literal true or false (§3.10.3), or a
character literal between '\u0000' and '\u007f' inclusive (§3.10.4), then let a
and b be the results of any two boxing conversions of p. It is always the case
that a == b.
However, there's no requirement that all these special literal values must be
created at system bootstrap time. So it's conceivable that IntegerCache may be
rewritten to create the object dynamically:
public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high) {
+ if (IntegerCache.cache[i + (-IntegerCache.low)] == null) {
+ IntegerCache.cache[i + (-IntegerCache.low)] = new Integer(i);
+ }
return IntegerCache.cache[i + (-IntegerCache.low)];
}
return new Integer(i);
}
Now, is this likely to happen? Probably not. However, in HotSpot, we should not
assume that the library will always stay the same, and that the library writer
knows what HotSpot requires.
So your suggestion was to add warnings specifically for Integer cache array.
Looks like I’ve given it a much deeper interpretation.
I’ll add a warning about the cache. Will send new webrev tomorrow.
Thanks,
Jiangli
Thanks
- Ioi
On 11/1/18 3:47 PM, Jiangli Zhou wrote:
Hi Ioi,
Thanks for the review. I renamed both fields as suggested and added a warning
for closed_archive_subgraph_entry_fields. A standalone warning message in
Integer.java could be overlooked, so I added
HeapShared::check_closed_archive_heap_region_object() for checking the
instances being included in the closed archive heap regions at dump time.
http://cr.openjdk.java.net/~jiangli/8212995/webrev.02/
Thanks,
Jiangli
On 10/31/18 8:52 PM, Ioi Lam wrote:
Hi Jiangli,
static ArchivableStaticFieldInfo shareable_subgraph_entry_fields[] = {...}
static ArchivableStaticFieldInfo subgraph_entry_fields[] = {...}
Maybe these should be renamed to {open/closed}_archive_subgraph_entry_fields?
Also, I think we should add a strong warning about what objects can be placed
in closed_archive_subgraph_entry_fields[]. Any references stored in these
objects must not be modified at run time (or else we could have a pointer that
from the closed region to the outside, violating the properties of the closed
region.
Maybe we should also add a warning in Integer.java, something akin to "if you modify
this class, check to see if it can still meet the requirements in heapShared.cpp"?
The rest of the code seems OK to me.
As a future improvement, for all the objects whose fields are all
non-reference, final fields, maybe we can automatically put them in the closed
archive region? For example, all archived primitive box objects are in this
category.
Thanks
- Ioi
On 10/31/18 12:45 PM, Jiangli Zhou wrote:
On 10/31/18 12:08 PM, Jiangli Zhou wrote:
Hi Ioi,
Here is an updated webrev with renaming of the 'is_shared' argument. I decided
to go with your suggestion, 'is_closed_archive'.
http://cr.openjdk.java.net/~jiangli/8212995/webrev.01/
BTW, in above webrev, I also included a typo fix for the following warning that
Mandy found (thanks Mandy!)
@@ -1324,11 +1329,11 @@
// header data
const char* prop = Arguments::get_property("java.system.class.loader");
if (prop != NULL) {
warning("Archived non-system classes are disabled because the "
"java.system.class.loader property is specified (value = \"%s\").
"
- "To use archived non-system classes, this property must be not be
set", prop);
+ "To use archived non-system classes, this property must not be
set", prop);
_has_platform_or_app_classes = false;
}
Thanks,
Jiangli
Thanks,
Jiangli
On 10/30/18 4:19 PM, Jiangli Zhou wrote:
Hi Ioi,
On 10/30/18 3:00 PM, Ioi Lam wrote:
Hi Jiangli,
This looks promising.
Now a full review yet, but I am wondering about the name of the is_shared
parameter
void add_subgraph_entry_field(int static_field_offset, oop v, bool
is_shared);
Since this is part of "heapShared", everything is "shared" in some sense of the
word. It could be confusing to say something is more shared than other things which also shared ...
How "is_closed_archive" instead?
Yes, our 'shared' has broader meaning. "is_closed_archive" or "is_closed_space"
sounds good to me. I'll rename.
Thanks,
Jiangli
Thanks
- Ioi
On 10/30/2018 01:57 PM, Jiangli Zhou wrote:
Please review the following change for moving the archived Integer.IntegerCache
and it's cached Integer objects (256) to the closed archiving heap region. The
IntegerCache subgraph does not contain any reference that's changed at runtime
(good candidate for sharing). Moving the whole subgraph into the closed archive
heap region allows the memory to be shared by different JVM instances at
runtime. The saving is 4K per JVM instance running the same or different java
application simultaneously. Although 4K is not significant, in a larger picture
the saving is much bigger (4k * (JVM_instance_num - 1) * host_num).
As part of the change, I also restructured the code to allow us to plug in more
shareable subgraphs in the closed archive heap region for runtime footprint
saving in the future.
The 'st' space is renamed to 'ca' (closed archive) space since it now contains
other types of objects besides j.l.Strings.
webrev: http://cr.openjdk.java.net/~jiangli/8212995/webrev.00/
RFE: https://bugs.openjdk.java.net/browse/JDK-8212995
Before:
mc space: 8416 [ 0.0% of total] out of 12288 bytes [ 68.5% used] at
0x0000000800000000
rw space: 3946640 [ 21.4% of total] out of 3948544 bytes [100.0% used] at
0x0000000800003000
ro space: 7319328 [ 39.6% of total] out of 7319552 bytes [100.0% used] at
0x00000008003c7000
md space: 2416 [ 0.0% of total] out of 4096 bytes [ 59.0% used] at
0x0000000800ac2000
od space: 6475944 [ 35.0% of total] out of 6479872 bytes [ 99.9% used] at
0x0000000800ac3000
st0 space: 438272 [ 2.4% of total] out of 438272 bytes [100.0% used] at 0x00000007ffc00000
<<<<<<<<<<
oa0 space: 282624 [ 1.5% of total] out of 282624 bytes [100.0% used] at 0x00000007ff800000
<<<<<<<<<<
total : 18473640 [100.0% of total] out of 18485248 bytes [ 99.9% used]
After:
mc space: 8416 [ 0.0% of total] out of 12288 bytes [ 68.5% used] at
0x0000000800000000
rw space: 3946640 [ 21.4% of total] out of 3948544 bytes [100.0% used] at
0x0000000800003000
ro space: 7319304 [ 39.6% of total] out of 7319552 bytes [100.0% used] at
0x00000008003c7000
md space: 2416 [ 0.0% of total] out of 4096 bytes [ 59.0% used] at
0x0000000800ac2000
od space: 6475920 [ 35.0% of total] out of 6479872 bytes [ 99.9% used] at
0x0000000800ac3000
ca0 space: 442368 [ 2.4% of total] out of 442368 bytes [100.0% used] at 0x00000007ffc00000
<<<<<<<<<<
oa0 space: 278528 [ 1.5% of total] out of 278528 bytes [100.0% used] at 0x00000007ff800000
<<<<<<<<<<
total : 18473592 [100.0% of total] out of 18485248 bytes [ 99.9% used]
Tested with appcds tests on linux-x64 locally. Running tier1-teir4 tests.
Thanks,
Jiangli
