<s>
Readahead	B-Application
is	O
a	O
system	B-Operating_System
call	I-Operating_System
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
that	O
loads	O
a	O
file	O
's	O
contents	O
into	O
the	O
page	B-General_Concept
cache	I-General_Concept
.	O
</s>
<s>
This	O
prefetches	B-General_Concept
the	O
file	O
so	O
that	O
when	O
it	O
is	O
subsequently	O
accessed	O
,	O
its	O
contents	O
are	O
read	O
from	O
the	O
main	O
memory	O
(	O
RAM	B-Architecture
)	O
rather	O
than	O
from	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
HDD	O
)	O
,	O
resulting	O
in	O
much	O
lower	O
file	O
access	O
latencies	O
.	O
</s>
<s>
Many	O
Linux	B-Application
distributions	I-Application
use	O
readahead	B-Application
on	O
a	O
list	O
of	O
commonly	O
used	O
files	O
to	O
speed	O
up	O
booting	B-Operating_System
.	O
</s>
<s>
In	O
such	O
a	O
setup	O
,	O
if	O
the	O
kernel	B-Operating_System
is	O
booted	O
with	O
the	O
boot	B-Operating_System
parameter	O
,	O
it	O
will	O
record	O
all	O
file	O
accesses	O
during	O
bootup	B-Operating_System
and	O
write	O
a	O
new	O
list	O
of	O
files	O
to	O
be	O
read	O
during	O
later	O
boot	B-Operating_System
sequences	I-Operating_System
.	O
</s>
<s>
This	O
will	O
make	O
additional	O
installed	O
services	O
start	O
faster	O
,	O
because	O
they	O
are	O
not	O
included	O
in	O
the	O
default	O
readahead	B-Application
list	O
.	O
</s>
<s>
In	O
Linux	B-Application
distributions	I-Application
that	O
use	O
systemd	B-Application
,	O
readahead	B-Application
binary	O
(	O
as	O
part	O
of	O
the	O
boot	B-Operating_System
sequence	I-Operating_System
)	O
was	O
replaced	O
by	O
systemd-readahead	B-Application
.	O
</s>
<s>
However	O
,	O
support	O
for	O
readahead	B-Application
was	O
removed	O
from	O
systemd	B-Application
in	O
its	O
version	O
217	O
,	O
being	O
described	O
as	O
unmaintained	O
and	O
unable	O
to	O
provide	O
expected	O
performance	O
benefits	O
.	O
</s>
<s>
Certain	O
experimental	O
page-level	O
prefetching	B-General_Concept
systems	O
have	O
been	O
developed	O
to	O
further	O
improve	O
performance	O
.	O
</s>
<s>
Bcache	B-Application
support	O
readahead	B-Application
of	O
files	O
and	O
metadata	O
.	O
</s>
<s>
ZFS	B-Application
supports	O
readahead	B-Application
of	O
files	O
and	O
metadata	O
,	O
when	O
using	O
ARC	O
.	O
</s>
