<s>
In	O
computing	O
,	O
process	B-Operating_System
migration	I-Operating_System
is	O
a	O
specialized	O
form	O
of	O
process	B-Operating_System
management	I-Operating_System
whereby	O
processes	B-Operating_System
are	O
moved	O
from	O
one	O
computing	O
environment	O
to	O
another	O
.	O
</s>
<s>
This	O
originated	O
in	O
distributed	B-Architecture
computing	I-Architecture
,	O
but	O
is	O
now	O
used	O
more	O
widely	O
.	O
</s>
<s>
On	O
multicore	B-Architecture
machines	O
(	O
multiple	O
cores	O
on	O
one	O
processor	O
or	O
multiple	O
processors	O
)	O
process	B-Operating_System
migration	I-Operating_System
happens	O
as	O
a	O
standard	O
part	O
of	O
process	O
scheduling	O
,	O
and	O
it	O
is	O
quite	O
easy	O
to	O
migrate	O
a	O
process	O
within	O
a	O
given	O
machine	O
,	O
since	O
most	O
resources	O
(	O
memory	O
,	O
files	O
,	O
sockets	O
)	O
do	O
not	O
need	O
to	O
be	O
changed	O
,	O
only	O
the	O
execution	O
context	O
(	O
primarily	O
program	B-General_Concept
counter	I-General_Concept
and	O
registers	O
)	O
.	O
</s>
<s>
The	O
traditional	O
form	O
of	O
process	B-Operating_System
migration	I-Operating_System
is	O
in	O
computer	B-Architecture
clusters	I-Architecture
where	O
processes	B-Operating_System
are	O
moved	O
from	O
machine	O
to	O
machine	O
,	O
which	O
is	O
significantly	O
more	O
difficult	O
,	O
as	O
it	O
requires	O
serializing	O
the	O
process	O
image	O
and	O
migrating	O
or	O
reacquiring	O
resources	O
at	O
the	O
new	O
machine	O
.	O
</s>
<s>
The	O
first	O
implementation	O
of	O
process	B-Operating_System
migration	I-Operating_System
was	O
in	O
the	O
DEMOS/MP	O
operating	O
project	O
at	O
the	O
University	O
of	O
California	O
,	O
Berkeley	O
and	O
was	O
described	O
in	O
a	O
1983	O
paper	O
by	O
Barton	O
Miller	O
and	O
Michael	O
Powell	O
.	O
</s>
<s>
Process	B-Operating_System
migration	I-Operating_System
is	O
implemented	O
in	O
,	O
among	O
others	O
,	O
OpenMosix	B-Operating_System
and	O
the	O
Sprite	B-Operating_System
OS	I-Operating_System
from	O
the	O
University	O
of	O
California	O
,	O
Berkeley	O
.	O
</s>
<s>
Process	B-Operating_System
migration	I-Operating_System
in	O
computing	O
comes	O
in	O
two	O
flavors	O
:	O
</s>
<s>
Non-preemptive	O
process	B-Operating_System
migration	I-Operating_System
Process	B-Operating_System
migration	I-Operating_System
that	O
takes	O
place	O
before	O
execution	O
of	O
the	O
process	O
starts	O
(	O
i.e.	O
</s>
<s>
migration	O
whereby	O
a	O
process	O
need	O
not	O
be	O
preempted	B-Operating_System
)	O
.	O
</s>
<s>
This	O
type	O
of	O
process	B-Operating_System
migration	I-Operating_System
is	O
relatively	O
cheap	O
,	O
since	O
relatively	O
little	O
administrative	O
overhead	O
is	O
involved	O
.	O
</s>
<s>
Preemptive	B-Operating_System
process	I-Operating_System
migration	I-Operating_System
Process	B-Operating_System
migration	I-Operating_System
whereby	O
a	O
process	O
is	O
preempted	B-Operating_System
,	O
migrated	O
and	O
continues	O
processing	O
in	O
a	O
different	O
execution	O
environment	O
.	O
</s>
<s>
This	O
type	O
of	O
process	B-Operating_System
migration	I-Operating_System
is	O
relatively	O
expensive	O
,	O
since	O
it	O
involves	O
recording	O
,	O
migration	O
and	O
recreation	O
of	O
the	O
process	O
state	O
as	O
well	O
as	O
the	O
reconstructing	O
of	O
any	O
inter-process	B-Operating_System
communication	I-Operating_System
channels	O
to	O
which	O
the	O
migrating	O
process	O
is	O
connected	O
.	O
</s>
<s>
Inter-process	B-Operating_System
communication	I-Operating_System
:	O
</s>
<s>
The	O
machine	O
the	O
process	O
migrated	O
away	O
from	O
needs	O
to	O
keep	O
records	O
of	O
migrated	O
processes	B-Operating_System
.	O
</s>
<s>
Shared	B-Operating_System
memory	I-Operating_System
:	O
</s>
<s>
if	O
one	O
of	O
a	O
group	O
of	O
cooperating	O
processes	B-Operating_System
migrates	O
away	O
and	O
all	O
these	O
processes	B-Operating_System
use	O
a	O
shared	B-Operating_System
memory	I-Operating_System
segment	O
,	O
then	O
the	O
network	O
must	O
be	O
used	O
to	O
emulate	O
shared	B-Operating_System
memory	I-Operating_System
access	O
.	O
</s>
<s>
This	O
adds	O
complexity	O
and	O
slows	O
down	O
access	O
to	O
the	O
shared	B-Operating_System
memory	I-Operating_System
dramatically	O
for	O
processes	B-Operating_System
that	O
migrated	O
away	O
from	O
the	O
machine	O
holding	O
the	O
shared	B-Operating_System
memory	I-Operating_System
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
problems	O
mentioned	O
above	O
,	O
process	O
based	O
operating	O
systems	O
usually	O
maintain	O
a	O
variety	O
of	O
tables	O
and	O
states	O
for	O
running	O
processes	B-Operating_System
.	O
</s>
<s>
An	O
alternate	O
definition	O
of	O
process	B-Operating_System
migration	I-Operating_System
is	O
used	O
in	O
integrated	O
circuit	O
design	O
and	O
engineering	O
.	O
</s>
<s>
Process	B-Operating_System
migration	I-Operating_System
or	O
layout	O
migration	O
in	O
this	O
context	O
is	O
a	O
design	O
flow	O
to	O
change	O
and	O
shrink	O
an	O
existing	O
IC	O
layout	O
to	O
a	O
new	O
process	O
technology	O
node	O
.	O
</s>
<s>
The	O
implementation	O
of	O
a	O
process	B-Operating_System
migration	I-Operating_System
could	O
be	O
done	O
manually	O
by	O
redrawing	O
the	O
layout	O
feature	O
by	O
feature	O
or	O
by	O
automatic	O
EDA/CAD	O
tools	O
.	O
</s>
<s>
In	O
load	O
sharing	O
systems	O
,	O
a	O
process	O
is	O
migrated	O
from	O
one	O
node	O
to	O
another	O
using	O
a	O
mechanism	O
called	O
process	B-Operating_System
migration	I-Operating_System
.	O
</s>
<s>
The	O
concept	O
of	O
a	O
process	O
is	O
not	O
introduced	O
in	O
this	O
report	O
as	O
processes	B-Operating_System
are	O
a	O
well-known	O
design	O
in	O
operating	O
systems	O
.	O
</s>
<s>
Process	B-Operating_System
Migration	I-Operating_System
refers	O
to	O
the	O
mobility	O
of	O
executing	O
(	O
or	O
suspended	O
)	O
processes	B-Operating_System
in	O
a	O
distributed	B-Architecture
computing	I-Architecture
environment	O
.	O
</s>
