Weldon Washburn wrote:
On 7/11/06, Robin Garner <[EMAIL PROTECTED]> wrote:
Salikh Zakirov wrote:
> Ivan Volosyuk wrote:
>
>> My idea here, is if the function is required by VM, it can be
emulated
>> on VM side via "alloc + pin". Of cause, it is not the same as
>> gc_pinned_alloc. The behaviour of GC will be suboptimal in that case.
>>
>
> In fact, gc_alloc_pinned() is not intended to be equivalent to
gc_alloc()
> followed by gc_pin() for the following reasons
>
> 1) gc_pin() is optional operation, and may be absent in simplest
collectors
> 2) gc_pin() is not required to succeed, and the GC may decide to
reject
> object pinning (e.g. based on some memory footprint/performance
compromise).
> The success of operation must be checked by using
gc_is_object_pinned()
> 3) gc_alloc_pinned() may be implemented in a much more efficient
way than
> pinning of arbitrary object, e.g. by introducing the separate
fixed space
> with size-segregated lists or other malloc-like management
algorithms.
>
>
Perhaps a more relevant discussion is exactly what
hints/suggestions/requirements the VM and MM give each other on an
allocation request. MMTk allows the VM to explicitly request allocation
in a specific space, and this can/has been used to implement
optimizations such as pre-tenuring.
Yes! I like it :)
IMO a good high-performance
interface should at least allow the VM to provide a variety of hints to
the MM.
Yes! I hope you can help us define these performance hint APIs.
The ones I *know* are useful are:
- Immobile (object will never move)
- Mature (for pretenuring, full-heap GC ignores)
I could speculate about a bunch of other useful hints (eg hot/cold,
thread local, large/small ...), but probably nowhere near exhaustively -
probably best to simply create the mechanism, define a couple of hints
and leave it open for future use.
-- Robin
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