<s>
LogFS	B-Application
is	O
a	O
Linux	B-Operating_System
log-structured	B-Application
and	O
scalable	B-Architecture
flash	B-Application
file	I-Application
system	I-Application
,	O
intended	O
for	O
use	O
on	O
large	O
devices	O
of	O
flash	B-Device
memory	I-Device
.	O
</s>
<s>
It	O
is	O
written	O
by	O
Jörn	O
Engel	O
and	O
in	O
part	O
sponsored	O
by	O
the	O
CE	O
Linux	B-Operating_System
Forum	O
.	O
</s>
<s>
LogFS	B-Application
was	O
introduced	O
in	O
the	O
mainline	O
Linux	B-Operating_System
kernel	I-Operating_System
in	O
version	O
2.6.34	O
,	O
released	O
on	O
May	O
16	O
,	O
2010	O
.	O
</s>
<s>
It	O
was	O
removed	O
from	O
the	O
codebase	O
during	O
the	O
merge	B-Application
window	I-Application
of	O
version	O
4.10	O
,	O
in	O
December	O
2016	O
,	O
because	O
it	O
was	O
"	O
unmaintained	O
for	O
years	O
and	O
seemingly	O
unused	O
"	O
.	O
</s>
<s>
,	O
LogFS	B-Application
was	O
mature	O
enough	O
to	O
pass	O
its	O
entire	O
test	O
suite	O
,	O
and	O
was	O
subsequently	O
included	O
in	O
the	O
mainline	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
marked	O
as	O
'	O
experimental	O
 '	O
,	O
in	O
version	O
2.6.34	O
released	O
on	O
May	O
16	O
,	O
2010	O
.	O
</s>
<s>
However	O
,	O
it	O
did	O
not	O
attract	O
a	O
large	O
user	O
base	O
and	O
was	O
removed	O
from	O
the	O
kernel	B-Operating_System
in	O
December	O
2016	O
.	O
</s>
<s>
LogFS	B-Application
was	O
motivated	O
by	O
the	O
difficulties	O
of	O
JFFS2	O
with	O
larger	O
flash-memory	O
drives	O
.	O
</s>
<s>
LogFS	B-Application
stores	O
the	O
inode	B-Application
tree	I-Application
on	O
the	O
drive	O
;	O
JFFS2	O
does	O
not	O
,	O
which	O
requires	O
it	O
to	O
scan	O
the	O
entire	O
drive	O
at	O
mount	O
and	O
cache	B-General_Concept
the	O
entire	O
tree	O
in	O
RAM	O
.	O
</s>
<s>
LogFS	B-Application
avoids	O
these	O
penalties	O
,	O
but	O
it	O
does	O
do	O
more	O
work	O
while	O
the	O
system	O
is	O
running	O
and	O
uses	O
some	O
of	O
the	O
drive	O
's	O
space	O
for	O
holding	O
the	O
inode	B-Application
tree	I-Application
.	O
</s>
<s>
LogFS	B-Application
stores	O
a	O
file	O
's	O
inode	B-Application
tree	I-Application
on	O
the	O
drive	O
,	O
which	O
means	O
on	O
a	O
write	O
to	O
the	O
file	O
,	O
each	O
ancestor	O
node	O
in	O
the	O
tree	O
must	O
be	O
rewritten	O
.	O
</s>
<s>
Writing	O
the	O
root	O
last	O
maintains	O
atomicity	B-General_Concept
of	O
the	O
update	O
.	O
</s>
<s>
LogFS	B-Application
handles	O
this	O
disparity	O
by	O
packing	O
multiple	O
file-system	O
blocks	O
into	O
a	O
single	O
flash-memory	O
block	O
.	O
</s>
<s>
LogFS	B-Application
's	O
garbage	O
collection	O
strategy	O
relies	O
on	O
file	O
data	O
being	O
placed	O
in	O
a	O
certain	O
way	O
into	O
flash-memory	O
blocks	O
:	O
a	O
flash-memory	O
block	O
will	O
hold	O
only	O
file	O
data	O
from	O
the	O
same	O
level	O
in	O
the	O
inode	B-Application
tree	I-Application
.	O
</s>
<s>
LogFS	B-Application
can	O
garbage	O
collect	O
the	O
top	O
level	O
of	O
the	O
trees	O
using	O
just	O
1	O
empty	O
flash-memory	O
block	O
.	O
</s>
<s>
And	O
can	O
garbage	O
collect	O
all	O
N	O
levels	O
of	O
the	O
trees	O
using	O
N	O
empty	O
flash	B-Device
memory	I-Device
blocks	O
.	O
</s>
