Re: Reduce XFS footprint (was Re: TAKE - remove a function xfs added to filemap.c

[Stephen Lord <lord@xxxxxxx>]

Ralf G. R. Bergs wrote:

> > then it gets a bit smaller. There are definitely other code paths you 
> > cannot get to in there
> > which we could cut out - just a matter of finding them.
>
> That reminds me of another question I'm asking myself since a while: It seems 
> as if you're developing XFS for Linux from scratch instead of "just" porting 
> it from SGI. Is that right? Or why do you seem to change even fundamental code 
> pieces? Or does porting to Linux mean you have to rewrite it because it's so 
> different from IRIX?

I would say 95% of the code is untouched, except for the endian 
conversion work which
was neccessary for a little endian implementation. The interfaces 
between the vfs and
the filesystem and between the filesystem and the block layer are where 
all the
changes have happened. We did need to do a lot of work for data caching 
since the
Irix model and the linux model were not at all close. The vfs layer has 
some major
differences too.

> > You could try editing xfs_types.h and  changing
> >
> > #define XFS_BIG_FILES           1
> > #define XFS_BIG_FILESYSTEMS     1
> >
> > to
> >
> > #define XFS_BIG_FILES           0
> > #define XFS_BIG_FILESYSTEMS    0
>
> I probably can't do that since as you know I use hardware RAIDs so I probably 
> need "big" filesystems, and I also need "big" files.

The limits in xfs if you turn these off are:

Max file size 2^40 bytes
Max filesystem size is 2 Tbytes I think (not sure without some research).

It does compile and run, and you save about 45K in code size by doing it,
so not too much. You can also edit xfs_macros.h and define WANT_SPACE_C
to 1 (replace the existing definition). This turns a lot of inline 
macros into
function calls - it will be slower, but it is another 10K less code - 
again, not
very much.

So  and smp build (in 2.5) went from

  text    data     bss     dec     hex filename
520994    4896    2080  527970   80e62 fs/xfs/xfs.o

to
  text    data     bss     dec     hex filename
487334    4896    2080  494310   78ae6 fs/xfs/xfs.o

with these two build changes.

Steve