<s>
Reiser4	B-Application
is	O
a	O
computer	B-Application
file	I-Application
system	I-Application
,	O
successor	O
to	O
the	O
ReiserFS	B-Application
file	B-Application
system	I-Application
,	O
developed	O
from	O
scratch	O
by	O
Namesys	O
and	O
sponsored	O
by	O
DARPA	O
as	O
well	O
as	O
Linspire	O
.	O
</s>
<s>
Reiser4	B-Application
was	O
named	O
after	O
its	O
former	O
lead	O
developer	O
Hans	O
Reiser	O
.	O
</s>
<s>
,	O
the	O
Reiser4	B-Application
patch	O
set	O
is	O
still	O
being	O
maintained	O
,	O
but	O
according	O
to	O
Phoronix	O
,	O
it	O
is	O
unlikely	O
to	O
be	O
merged	O
into	O
mainline	O
Linux	B-Operating_System
without	O
corporate	O
backing	O
.	O
</s>
<s>
Some	O
of	O
the	O
goals	O
of	O
the	O
Reiser4	B-Application
file	B-Application
system	I-Application
are	O
:	O
</s>
<s>
Some	O
of	O
the	O
more	O
advanced	O
Reiser4	B-Application
features	O
(	O
such	O
as	O
user-defined	O
transactions	B-General_Concept
)	O
are	O
also	O
not	O
available	O
because	O
of	O
a	O
lack	O
of	O
a	O
VFS	B-Application
API	O
for	O
them	O
.	O
</s>
<s>
At	O
present	O
Reiser4	B-Application
lacks	O
a	O
few	O
standard	O
file	B-Application
system	I-Application
features	O
,	O
such	O
as	O
an	O
online	O
repacker	O
(	O
similar	O
to	O
the	O
defragmentation	B-Application
utilities	O
provided	O
with	O
other	O
file	B-Application
systems	I-Application
)	O
.	O
</s>
<s>
The	O
creators	O
of	O
Reiser4	B-Application
say	O
they	O
will	O
implement	O
these	O
later	O
,	O
or	O
sooner	O
if	O
someone	O
pays	O
them	O
to	O
do	O
so	O
.	O
</s>
<s>
Reiser4	B-Application
uses	O
B*	O
-trees	O
in	O
conjunction	O
with	O
the	O
dancing	B-Data_Structure
tree	I-Data_Structure
balancing	O
approach	O
,	O
in	O
which	O
underpopulated	O
nodes	O
will	O
not	O
be	O
merged	O
until	O
a	O
flush	O
to	O
disk	O
except	O
under	O
memory	O
pressure	O
or	O
when	O
a	O
transaction	O
completes	O
.	O
</s>
<s>
Such	O
a	O
system	O
also	O
allows	O
Reiser4	B-Application
to	O
create	O
files	O
and	O
directories	B-Application
without	O
having	O
to	O
waste	O
time	O
and	O
space	O
through	O
fixed	O
blocks	O
.	O
</s>
<s>
,	O
synthetic	O
benchmarks	O
performed	O
by	O
Namesys	O
in	O
2003	O
show	O
that	O
Reiser4	B-Application
is	O
10	O
to	O
15	O
times	O
faster	O
than	O
its	O
most	O
serious	O
competitor	O
ext3	B-Application
working	O
on	O
files	O
smaller	O
than	O
1	O
KiB	O
.	O
</s>
<s>
Namesys	O
's	O
benchmarks	O
suggest	O
it	O
is	O
typically	O
twice	O
the	O
performance	O
of	O
ext3	B-Application
for	O
general-purpose	O
filesystem	B-Application
usage	O
patterns	O
.	O
</s>
<s>
Other	O
benchmarks	O
from	O
2006	O
show	O
results	O
of	O
Reiser4	B-Application
being	O
slower	O
on	O
many	O
operations	O
.	O
</s>
<s>
Benchmarks	O
conducted	O
in	O
2013	O
with	O
Linux	B-Operating_System
Kernel	I-Operating_System
version	O
3.10	O
show	O
that	O
Reiser4	B-Application
is	O
considerably	O
faster	O
in	O
various	O
tests	O
compared	O
to	O
in-kernel	O
filesystems	B-Application
ext4	B-Application
,	O
btrfs	B-Operating_System
and	O
XFS	B-Application
.	O
</s>
<s>
Reiser4	B-Application
has	O
patches	O
for	O
Linux	B-Operating_System
2.6	I-Operating_System
,	O
3.x	O
,	O
4.x	O
and	O
5.x.	O
,	O
but	O
,	O
Reiser4	B-Application
has	O
not	O
been	O
merged	O
into	O
the	O
mainline	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
consequently	O
is	O
still	O
not	O
supported	O
on	O
many	O
Linux	B-Application
distributions	I-Application
;	O
however	O
,	O
its	O
predecessor	O
ReiserFS	B-Application
v3	O
has	O
been	O
widely	O
adopted	O
.	O
</s>
<s>
Reiser4	B-Application
is	O
also	O
available	O
from	O
Andrew	O
Morton	O
's	O
-mm	B-Application
kernel	B-Operating_System
sources	O
,	O
and	O
from	O
Zen	O
patch	O
set	O
.	O
</s>
<s>
Linux	B-Operating_System
kernel	I-Operating_System
developers	O
claim	O
that	O
Reiser4	B-Application
does	O
not	O
follow	O
Linux	B-Operating_System
coding	O
standards	O
,	O
but	O
Hans	O
Reiser	O
suggested	O
political	O
reasons	O
.	O
</s>
<s>
Hans	O
Reiser	O
was	O
convicted	O
of	O
murder	O
on	O
April	O
28	O
,	O
2008	O
,	O
leaving	O
the	O
future	O
of	O
Reiser4	B-Application
uncertain	O
.	O
</s>
<s>
Shishkin	O
and	O
others	O
continued	O
the	O
development	O
of	O
Reiser4	B-Application
,	O
making	O
source	O
code	O
available	O
from	O
Shishkin	O
's	O
web	O
site	O
,	O
later	O
relocated	O
to	O
kernel.org	B-Application
.	O
</s>
<s>
In	O
2010	O
,	O
Phoronix	O
wrote	O
that	O
Edward	O
Shishkin	O
was	O
exploring	O
options	O
to	O
get	O
Reiser4	B-Application
merged	O
into	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
.	O
</s>
<s>
,	O
the	O
file	B-Application
system	I-Application
is	O
still	O
being	O
updated	O
for	O
new	O
kernel	B-Operating_System
releases	O
,	O
but	O
has	O
not	O
been	O
submitted	O
for	O
merging	O
.	O
</s>
<s>
In	O
2015	O
,	O
Michael	O
Larabel	O
mentioned	O
it	O
is	O
unlikely	O
to	O
happen	O
without	O
corporate	O
backing	O
,	O
and	O
then	O
he	O
suggested	O
in	O
April	O
2019	O
that	O
the	O
main	O
obstacle	O
could	O
be	O
the	O
renaming	O
of	O
Reiser4	B-Application
to	O
avoid	O
reference	O
to	O
the	O
initial	O
author	O
who	O
was	O
convicted	O
of	O
murder	O
.	O
</s>
<s>
Shishkin	O
announced	O
a	O
Reiser5	O
filesystem	B-Application
on	O
December	O
31	O
,	O
2019	O
.	O
</s>
