<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
coalescing	B-General_Concept
is	O
a	O
part	O
of	O
memory	B-General_Concept
management	I-General_Concept
in	O
which	O
two	O
adjacent	O
free	O
blocks	O
of	O
computer	B-General_Concept
memory	I-General_Concept
are	O
merged	O
.	O
</s>
<s>
When	O
a	O
program	B-Application
no	O
longer	O
requires	O
certain	O
blocks	O
of	O
memory	O
,	O
these	O
blocks	O
of	O
memory	O
can	O
be	O
freed	B-General_Concept
.	O
</s>
<s>
Without	O
coalescing	B-General_Concept
,	O
these	O
blocks	O
of	O
memory	O
stay	O
separate	O
from	O
each	O
other	O
in	O
their	O
original	O
requested	O
size	O
,	O
even	O
if	O
they	O
are	O
next	O
to	O
each	O
other	O
.	O
</s>
<s>
If	O
a	O
subsequent	O
request	O
for	O
memory	O
specifies	O
a	O
size	O
of	O
memory	O
that	O
cannot	O
be	O
met	O
with	O
an	O
integer	O
number	O
of	O
these	O
(	O
potentially	O
unequally-sized	O
)	O
freed	B-General_Concept
blocks	O
,	O
these	O
neighboring	O
blocks	O
of	O
freed	B-General_Concept
memory	O
cannot	O
be	O
allocated	O
for	O
this	O
request	O
.	O
</s>
<s>
Coalescing	B-General_Concept
alleviates	O
this	O
issue	O
by	O
setting	O
the	O
neighboring	O
blocks	O
of	O
freed	B-General_Concept
memory	O
to	O
be	O
contiguous	O
without	O
boundaries	O
,	O
such	O
that	O
part	O
or	O
all	O
of	O
it	O
can	O
be	O
allocated	O
for	O
the	O
request	O
.	O
</s>
<s>
Among	O
other	O
techniques	O
,	O
coalescing	B-General_Concept
is	O
used	O
to	O
reduce	O
external	B-Architecture
fragmentation	I-Architecture
,	O
but	O
is	O
not	O
totally	O
effective	O
.	O
</s>
<s>
Coalescing	B-General_Concept
can	O
be	O
done	O
as	O
soon	O
as	O
blocks	O
are	O
freed	B-General_Concept
,	O
or	O
it	O
can	O
be	O
deferred	O
until	O
some	O
time	O
later	O
(	O
known	O
as	O
deferred	O
coalescing	B-General_Concept
)	O
,	O
or	O
it	O
might	O
not	O
be	O
done	O
at	O
all	O
.	O
</s>
<s>
Coalescence	B-General_Concept
and	O
related	O
techniques	O
like	O
heap	B-General_Concept
compaction	I-General_Concept
,	O
can	O
be	O
used	O
in	O
garbage	B-General_Concept
collection	I-General_Concept
.	O
</s>
