[Vm-dev] [Pharo-dev] [NB] Trying to implement a ReadStream on NBExternalAddress

[Eliot Miranda]

Hi Henry,


On Wed, Sep 25, 2013 at 1:14 AM, Henrik Johansen <
henrik.s.johansen at veloxit.no> wrote:

>
>
> On Sep 24, 2013, at 9:58 , Eliot Miranda <eliot.miranda at gmail.com> wrote:
>
>
>
>
> On Mon, Sep 23, 2013 at 3:10 PM, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> wrote:
>
>> Isn't Eliot just implementing this feature, having a segment of non
>> relocatable objects?
>>
>
> Sort of.  Spur will allow any object in old space to stay still, and
> through become can move any object to old space very simply.  So instead of
> having a special fixed space segment it has a best-bit compaction algorithm
> that doesn't slide objects, but moves them into holes.  With this kind of
> compaction it is very easy to leave objects put.
>
> A further advantage of Spur is that objects have 64-bit alignment so
> passing arrays to e.g. code using sse instructions, won't cause potential
> alignment faults.
>
>
> Not to be a drag, but SSE operations have 16-byte alignment requirement.
> With 8-byte aligmnent of first indexable slot, you'd still need to use
> aligned loads/stores.
>

Talking out-of-line with someone who has lots of experience with Smalltalk
memory management it came to me that the pinning primitive could (and
should) take an aligmnet argument).  So one says e.g.

buffer := (ByteArray new: 1024) pinWithByteAlignment: 16

-- 
best,
Eliot
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