On 08/13/2012 11:04 PM, Theodore Ts'o wrote:
I had an idea which I think would make inline directories more
efficient, although it wouldn't be a backwards compatible change with
the existing patch sets to date.
that should be fine since we don't have much machines deployed by now.
We don't actually need to store the entry for '.', since we know what
that should be, and we could just store the parent directory in a
4-byte entry. By not storing the full directory entries for "." and
"..", we would save 20 bytes, which for a 256 byte inode where only
120 bytes or so are available for the inline directory, is pretty
significant. (We can just synthesize them for the benefit of readdir
and lookup --- and I'm pretty sure the VFS is doing its own synthesis
for "." and possibly ".." already as far as lookup is concerned.)
As andreas said in another e-mail, that would make the codes a little
complex. So in general, in my previous version, I just tried to refactor
most of the codes so that they can work for both inline inode and dir
blocks. But if these changes are merged, we have to re-write all of the
codes that are currently shared, such as ext4_find_entry, empty_dir,
ext4_add_entry etc.
Having said that, maybe it is worth the codes effort if we can see a
great improvement for inline dir. Since Andreas and you are both OK with
this new solution, I can try to re-work the inline data patch to support it.
Thanks
Tao