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Message-ID: <9623c9a50703220348h52661c99j1e160996c78cf3ff@mail.gmail.com>
Date: Thu, 22 Mar 2007 18:48:00 +0800
From: "Xiao-Feng Li" <xiaofeng.li@gmail.com>
To: dev@harmony.apache.org
Subject: Re: [DRLVM] what's the purpose to set NEXT_TO_HIGH_BIT_SET_MASK in
 object size?
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On 3/22/07, Pavel Pervov <pmcfirst@gmail.com> wrote:
> I mean, if there were three conditions to fall back to slow allocation and
> now there is only one such condition, is this right or it is the issue in
> harmony code which should be fixed ASAP?

Since finalizer is checked explicitly, the bit is never used at all.
In other words, it doesn't make sense to keep the useless constraint
bit in the code now.

This constraint bit is still set in the code. It confuses people and
requires GC to mask it to get the real allocation size.

Now there is only a few places in the code base manipulating this bit
(for nothing), it would be quite easy to remove them, unless there is
something I missed.

Thanks,
xiaofeng

> On 3/22/07, Pavel Pervov <pmcfirst@gmail.com> wrote:
> >
> > It is used in native override for Class.newInstance to overflow allocation
> > limit in fast path and fall back to slow allocation (which ignores this bit
> > set, as you've mentioned earlier). Class.newInstance is not native though
> > and this code simply does not work right now.
> >
> > The only property gc now treats as "not-possible-to-allocate-fast" is
> > "class has finalize method".
> > Is this correct from algorithmic POV?
> >
> > WBR,
> >     Pavel.
> >  On 3/22/07, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
> > >
> > > Pavel, thanks. Since the semantic of newInstance or alloc_instance or
> > > gc_alloc(_fast) itself doesn't actually use NEXT_TO_HIGH_BIT, no
> > > matter it is written in Java or other languages, I think NSO will not
> > > use it either. Do you think so? Or would you tell me how NSO will use
> > > NEXT_TO_HIGH_BIT?
> > >
> > > Thanks,
> > > xiaofeng
> > >
> > > On 3/21/07, Pavel Pervov < pmcfirst@gmail.com> wrote:
> > > > "is now implemented" it was supposed to be written. :)
> > > >
> > > > On 3/21/07, Pavel Pervov < pmcfirst@gmail.com> wrote:
> > > > >
> > > > > It is indirectly used in the NSO for Class.newInstance. But this
> > > code is
> > > > > not currently executed, since Class.newInstance is not implemented
> > > in
> > > > > Java.
> > > > >
> > > > > WBR,
> > > > >     Pavel.
> > > > > On 3/21/07, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
> > > > >
> > > > > > Pavel, Thanks for your reply.
> > > > > >
> > > > > > Would let me know how NEXT_TO_HIGH_BIT is used currently in DRLVM?
> > > Or
> > > > > > in other words, what functionalities are dependent on
> > > > > > NEXT_TO_HIGH_BIT?
> > > > > >
> > > > > > Thanks,
> > > > > > xiaofeng
> > > > > >
> > > > > > On 3/21/07, Pavel Pervov <pmcfirst@gmail.com> wrote:
> > > > > > > Xiao-Feng,
> > > > > > >
> > > > > > > All the infructructure is in place. It is just do not work at
> > > the
> > > > > > moment.
> > > > > > > As Class.newInstance is not native, NSO does not replace it's
> > > > > > implementation
> > > > > > > with VM's stub.
> > > > > > > If NEXT_TO_HIGH_BIT-supporting code is to be removed, the rest
> > > of the
> > > > > > code
> > > > > > > (NSO implementations for ia32 and ia64) has to be removed
> > > altogether
> > > > > > to not
> > > > > > > provoke any errors in the future.
> > > > > > >
> > > > > > > Does removing NSO overrides for Class.newInstance look
> > > reasonable for
> > > > > > you?
> > > > > > >
> > > > > > > WBR,
> > > > > > >     Pavel.
> > > > > > >
> > > > > > > On 3/21/07, Xiao-Feng Li <xiaofeng.li@gmail.com > wrote:
> > > > > > > >
> > > > > > > > If no one objects, I will try to remove this flag in DRLVM.
> > > > > > > >
> > > > > > > > Thanks,
> > > > > > > > xiaofeng
> > > > > > > >
> > > > > > > > On 3/21/07, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
> > > > > > > > > Hi, the source code for class preparation calls
> > > > > > > > > set_instance_data_size_constraint_bit() for three
> > > situations:
> > > > > > special
> > > > > > > > > alignment requirement, having finalizer, and to be pinned.
> > > And the
> > > > > > > > > comments there say the constraint bit is for GC to
> > > understand.
> > > > > > > > >
> > > > > > > > > But current GC actually doesn't care about this bit, and
> > > simply
> > > > > > masks
> > > > > > > > > it off. Does anybody know what are the situations for the
> > > size
> > > > > > > > > constraint bit to be set for allocation?
> > > > > > > > >
> > > > > > > > > I recall this kind of constraint bit was ORP legacy, when
> > > the
> > > > > > > > > intention was for gc_alloc_fast to be really fast, avoiding
> > > any
> > > > > > > > > special allocation treatment. So once the big flag is set,
> > > > > > > > > gc_alloc_fast will simply return NULL, and the VM will
> > > invoke
> > > > > > gc_alloc
> > > > > > > > > to accomplish the allocation.
> > > > > > > > >
> > > > > > > > > Now DRLVM has different processing, and the GC doesn't use
> > > the
> > > > > > flag in
> > > > > > > > > size for allocation. I wonder what is the real purpose of
> > > this
> > > > > > size
> > > > > > > > > flag in allocation.
> > > > > > > > >
> > > > > > > > > Thanks,
> > > > > > > > > xiaofeng
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > --
> > > > > > > Pavel Pervov,
> > > > > > > Intel Enterprise Solutions Software Division
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Pavel Pervov,
> > > > > Intel Enterprise Solutions Software Division
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Pavel Pervov,
> > > > Intel Enterprise Solutions Software Division
> > > >
> > >
> >
> >
> >
> > --
> > Pavel Pervov,
> > Intel Enterprise Solutions Software Division
> >
>
>
>
> --
> Pavel Pervov,
> Intel Enterprise Solutions Software Division
>