9 Mar
2023
9 Mar
'23
2:21 p.m.
I have not seen the UNIX kernel source code in quite a while, but as I
recall the double indirect block algorithm did not kick in until the file
exceeded a certain threshold. So it would not make sense to remove the code
for performance reasons.
Perhaps this is more likely due to the use of larger logical block sizes....
Is the code physically removed or IFDEF'd out for conditional compilation?
Perhaps someone decided that programmers would never need to test code on
large files..
On Wed, Mar 8, 2023, 8:10 AM Noel Chiappa <jnc(a)mercury.lcs.mit.edu> wrote:
In PWB1, support for 'huge' files appears to
have been removed. If one
compares bmap() in PWB1'S subr.c with V6's, the "'huge' fetch of
double
indirect block" code is gone. I guess PWB didn't need very large (>
8*256*512
= 1,048,576 bytes) files? I'm not sure what the _benefits_ of removing it
were, though - unless PWB was generating lots of files of between 7*256*512
and 8*256*512 bytes in length, and they wanted to avoid the overhead of the
double-indirect block? (The savings in code space are derisory - unlike in
LSX/MINI-UNIX.) Anyone know?
Noel