<s>
The	O
Orlov	B-Application
block	I-Application
allocator	I-Application
is	O
an	O
algorithm	O
to	O
define	O
where	O
a	O
particular	O
file	B-Operating_System
will	O
reside	O
on	O
a	O
given	O
file	B-Application
system	I-Application
(	O
blockwise	O
)	O
,	O
so	O
as	O
to	O
speed	O
up	O
disk	O
operations	O
.	O
</s>
<s>
The	O
scheme	O
is	O
named	O
after	O
its	O
creator	O
Grigoriy	O
Orlov	O
,	O
who	O
first	O
posted	O
,	O
in	O
2000	O
,	O
a	O
brief	O
description	O
and	O
implementation	O
for	O
OpenBSD	B-Operating_System
of	O
the	O
technique	O
,	O
which	O
was	O
later	O
used	O
in	O
the	O
BSD	B-Operating_System
Fast	O
Filesystem	B-Application
kernel	B-Operating_System
variants	O
.	O
</s>
<s>
The	O
performance	O
of	O
a	O
file	B-Application
system	I-Application
is	O
dependent	O
on	O
many	O
things	O
;	O
one	O
of	O
the	O
crucial	O
factors	O
is	O
just	O
how	O
that	O
filesystem	B-Application
lays	O
out	O
files	O
on	O
the	O
disk	O
.	O
</s>
<s>
The	O
Linux	O
ext2	B-Application
and	O
ext3	B-Application
filesystems	I-Application
,	O
for	O
instance	O
,	O
have	O
tried	O
to	O
spread	O
directories	O
on	O
the	O
cylinders	O
of	O
the	O
disk	O
.	O
</s>
<s>
Imagine	O
setting	O
up	O
a	O
system	O
with	O
users	O
 '	O
home	B-Application
directories	I-Application
in	O
/home	B-Application
:	O
if	O
all	O
the	O
first-level	O
directories	O
within	O
/home	B-Application
(	O
i.e.	O
</s>
<s>
the	O
home	B-Application
directories	I-Application
for	O
numerous	O
users	O
)	O
are	O
placed	O
next	O
to	O
each	O
other	O
,	O
there	O
may	O
be	O
no	O
space	O
left	O
for	O
the	O
contents	O
of	O
those	O
directories	O
.	O
</s>
<s>
Directories	O
created	O
in	O
the	O
root	O
directory	O
of	O
a	O
filesystem	B-Application
are	O
considered	O
top-level	O
directories	O
;	O
Theodore	O
Ts'o	O
added	O
a	O
special	O
inode	B-Application
flag	O
that	O
allows	O
the	O
system	O
administrator	O
to	O
mark	O
other	O
directories	O
as	O
being	O
top-level	O
directories	O
as	O
well	O
.	O
</s>
<s>
If	O
/home	B-Application
lives	O
in	O
the	O
root	O
filesystem	B-Application
,	O
a	O
simple	O
chattr	O
command	O
will	O
make	O
the	O
system	O
treat	O
it	O
as	O
a	O
top-level	O
directory	O
.	O
</s>
<s>
A	O
little	O
more	O
care	O
is	O
taken	O
,	O
however	O
,	O
to	O
ensure	O
that	O
the	O
directory	O
's	O
contents	O
will	O
also	O
be	O
able	O
to	O
fit	O
into	O
that	O
cylinder	O
group	O
;	O
if	O
there	O
are	O
not	O
many	O
inodes	B-Application
or	O
blocks	O
available	O
in	O
the	O
group	O
,	O
the	O
directory	O
will	O
be	O
placed	O
in	O
a	O
different	O
cylinder	O
group	O
that	O
has	O
more	O
resources	O
available	O
.	O
</s>
<s>
The	O
Orlov	B-Application
block	I-Application
allocator	I-Application
was	O
shown	O
to	O
offer	O
performance	O
gains	O
on	O
workloads	O
that	O
traverse	O
directory	O
trees	O
on	O
FreeBSD	O
.	O
</s>
<s>
,	O
only	O
one	O
benchmark	O
result	O
for	O
ext3	B-Application
,	O
using	O
the	O
allocator	O
seems	O
to	O
have	O
been	O
posted	O
.	O
</s>
<s>
The	O
results	O
are	O
promising	O
:	O
the	O
time	O
required	O
to	O
traverse	O
through	O
a	O
Linux	O
kernel	B-Operating_System
tree	O
was	O
reduced	O
by	O
roughly	O
30%	O
.	O
</s>
<s>
The	O
Orlov	O
scheme	O
needs	O
more	O
rigorous	O
benchmarking	O
;	O
it	O
also	O
needs	O
some	O
serious	O
stress	O
testing	O
to	O
demonstrate	O
that	O
performance	O
does	O
not	O
degrade	O
as	O
the	O
filesystem	B-Application
is	O
changed	O
over	O
time	O
.	O
</s>
