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Posted to dev@harmony.apache.org by Weldon Washburn <we...@gmail.com> on 2006/08/29 06:48:30 UTC
[DRLVM][MMTk GC] marksweep configuration works in "user mode"
All,
I just committed mods that allow MMTk marksweep configuration to run
the simple tests in test.java.
There were some workarounds in MMTk code itself. It does not make
sense to commit these workarounds to drlvm/trunk or to put them in
JIRA. Instead, I told Steve Blackburn what the MMTk porting problems
are.
For the record the MMTk mods are:
1)
SegregatedFreeList.java wants to use vmmagic atomic operations even in
single java thread app. But vmmagic atomic ops are not fully
functional in Jitrino.JET just yet. The workaround is to do a simple
write to memory instead of CAS. The mods to SegregatedFreeList.java
are:
731a732
> atomic = false; //wjw hack around Addresss.attempt bug
2)
MMType.getSlot() is hard coded to assume that element zero is an
"Offset" of zero from the vtable ptr. While this may indeed be the
case for JikesRVM, in DRLVM the offset is 12. The diff to MMType.java
is:
83,86c83,86
< if (isReferenceArray)
< return addr.plus(arrayOffset).plus(reference << LOG_BYTES_IN_ADDRESS);
< else
< return addr.plus(offsets[reference]);
---
> if (isReferenceArray)
> return addr.plus(12).plus(reference << LOG_BYTES_IN_ADDRESS); // return addr.plus(arrayOffset).plus(reference << LOG_BYTES_IN_ADDRESS);
> else
> return addr.plus(offsets[reference]);
--
Weldon Washburn
Intel Middleware Products Division
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Re: [DRLVM][MMTk GC] marksweep configuration works in "user mode"
Posted by Weldon Washburn <we...@gmail.com>.
The selection of header bits for object hash is controlled by HASH_MASK
located in mon_enter_exit.h. By happy coincidence, there was an unused bit
in the header. The old version:
#define HASH_MASK 0x7e
The hacked on version for MMTk:
#define HASH_MASK 0xfc
A question for those who know the thread manager code. Will the above cause
a problem today? Will it cause a problem with what the thread manager wants
to do with header bits tomorrow?
Now the semispace collector definitely goes further before it falls down. I
had a long IM session with Steve Blackburn (MMTk expert) last night to
figure out the next debug steps. We realized a few important items but, of
course, none of this is recorded in harmony-dev email. I will start a
second mmtk thread to record the current state of MMTk debugging.
On 8/29/06, Geir Magnusson Jr. <ge...@pobox.com> wrote:
>
>
>
> Weldon Washburn wrote:
> > On 8/29/06, Geir Magnusson Jr. <ge...@pobox.com> wrote:
> >>
> >>
> >> Weldon Washburn wrote:
> >> > All,
> >> >
> >> > I just committed mods that allow MMTk marksweep configuration to run
> >> > the simple tests in test.java.
> >> >
> >>
> >> That's cool - what do we do with it next? :)
> >
> > The next step is to get MMTk semispace collector running. I am
> > working on it right now. It turns out MMTk needs the mark bit and the
> > forwarding bit adjacent to each other in the same byte of the object
> > header. This may mean shoving around the bits in DRLVM object header
> > to get the required space.
>
> In neither case is it configurable via a mask or something?
>
> >
> >>
> >> geir
> >
>
> ---------------------------------------------------------------------
> Terms of use : http://incubator.apache.org/harmony/mailing.html
> To unsubscribe, e-mail: harmony-dev-unsubscribe@incubator.apache.org
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>
>
--
Weldon Washburn
Intel Middleware Products Division
Re: [DRLVM][MMTk GC] marksweep configuration works in "user mode"
Posted by "Geir Magnusson Jr." <ge...@pobox.com>.
Weldon Washburn wrote:
> On 8/29/06, Geir Magnusson Jr. <ge...@pobox.com> wrote:
>>
>>
>> Weldon Washburn wrote:
>> > All,
>> >
>> > I just committed mods that allow MMTk marksweep configuration to run
>> > the simple tests in test.java.
>> >
>>
>> That's cool - what do we do with it next? :)
>
> The next step is to get MMTk semispace collector running. I am
> working on it right now. It turns out MMTk needs the mark bit and the
> forwarding bit adjacent to each other in the same byte of the object
> header. This may mean shoving around the bits in DRLVM object header
> to get the required space.
In neither case is it configurable via a mask or something?
>
>>
>> geir
>
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Re: [DRLVM][MMTk GC] marksweep configuration works in "user mode"
Posted by Weldon Washburn <we...@gmail.com>.
On 8/29/06, Geir Magnusson Jr. <ge...@pobox.com> wrote:
>
>
> Weldon Washburn wrote:
> > All,
> >
> > I just committed mods that allow MMTk marksweep configuration to run
> > the simple tests in test.java.
> >
>
> That's cool - what do we do with it next? :)
The next step is to get MMTk semispace collector running. I am
working on it right now. It turns out MMTk needs the mark bit and the
forwarding bit adjacent to each other in the same byte of the object
header. This may mean shoving around the bits in DRLVM object header
to get the required space.
>
> geir
--
Weldon Washburn
Intel Middleware Products Division
---------------------------------------------------------------------
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Re: [DRLVM][MMTk GC] marksweep configuration works in "user mode"
Posted by "Geir Magnusson Jr." <ge...@pobox.com>.
Weldon Washburn wrote:
> All,
>
> I just committed mods that allow MMTk marksweep configuration to run
> the simple tests in test.java.
>
That's cool - what do we do with it next? :)
geir
> There were some workarounds in MMTk code itself. It does not make
> sense to commit these workarounds to drlvm/trunk or to put them in
> JIRA. Instead, I told Steve Blackburn what the MMTk porting problems
> are.
>
> For the record the MMTk mods are:
>
> 1)
> SegregatedFreeList.java wants to use vmmagic atomic operations even in
> single java thread app. But vmmagic atomic ops are not fully
> functional in Jitrino.JET just yet. The workaround is to do a simple
> write to memory instead of CAS. The mods to SegregatedFreeList.java
> are:
> 731a732
>> atomic = false; //wjw hack around Addresss.attempt bug
>
> 2)
> MMType.getSlot() is hard coded to assume that element zero is an
> "Offset" of zero from the vtable ptr. While this may indeed be the
> case for JikesRVM, in DRLVM the offset is 12. The diff to MMType.java
> is:
> 83,86c83,86
> < if (isReferenceArray)
> < return addr.plus(arrayOffset).plus(reference <<
> LOG_BYTES_IN_ADDRESS);
> < else
> < return addr.plus(offsets[reference]);
> ---
>> if (isReferenceArray)
>> return addr.plus(12).plus(reference <<
>> LOG_BYTES_IN_ADDRESS); // return
>> addr.plus(arrayOffset).plus(reference << LOG_BYTES_IN_ADDRESS);
>> else
>> return addr.plus(offsets[reference]);
>
>
>
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