Re: [PATCH] ext2 cleanups

[Andreas Dilger <adilger@turbolinux.com>]

Alan writes:
> > This patch cleans up the ext2 code in various places.  It is mostly cosmetic
> > changes to comments, avoiding lines > 80 columns, removing redundant #ifdef
> > lines, etc.  It also adds the new COMPAT flags from the current e2fsprogs
> > into include/linux/ext2_fs.h.
> 
> Any reason for not delaying this until 2.5.0 ? (ie any bug fixes)

No, it is cosmetic only (OK, the wrong block is reported as being cleared
if there is an error in ext2_free_blocks(), but that isn't much of a bug.

Neither is the 4 bytes wasted in ext2_inode_info by not_used_1, but in
the -ac kernels ext2 is the largest inode struct now that NFS is out
(AFAIK), so if you remove ext2 not_used_1, i_new_inode, i_osync, and put
i_prealloc_count into the 16 bits freed by i_osync, along with removing
i_attr_flags you can pack 10 struct inodes into a page instead of 9.
Note that the current patch does not do all of that yet.

Having 10% fewer pages for inodes would save me 142*4k = 568kB of RAM
on the system I'm writing this on, and frequently more as you can get
a LOT of cached inodes when running updatedb or a tar or similar.

<rant>
For that matter, there is a lot of cruft in struct inode that could be
in a union (e.g. you can't truncate, or have quotas on a pipe, block,
or char dev, and you don't need i_blocks in this case either, and you
only need i_dnotify for directories (I think i_zombie also), i_flock
for files, etc).  That is too much for 2.4, however, and will wait for
2.5 if there is support for this.  This would go along with fs-private
data in slab cache so that you don't need to pay a penalty for the worst
filesystem even if you don't use it.
</rant>

Cheers, Andreas
-- 
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert