Re: ext2/3 subdirectory limit [WAS: Choosing and tuning Linux file systems]

[Tomas Hruby <thruby@few.vu.nl>]

On Mon, Jun 26, 2006 at 02:59:00PM +0200, Erik Mouw wrote:
> On Mon, Jun 26, 2006 at 02:36:35PM +0200, Tomas Hruby wrote:
> > > > More than ~32,000 files in one directory: XFS or reiser
> > > 
> > > Ext3 can easily have more than 32000 *files* in a directory. However,
> > > it can only have 32000 *subdirectories* in a directory. This limit is
> > > from struct ext3_inode->i_links_count, which is an __le16: each
> > > subdirectory has an entry ".." that links back to its parent increasing
> > > the parents i_links_count.
> > 
> > I was always wondering why it increases link_count of the parent directory when
> > creating a subdirectory. It is clear that .. points to the parent, but the
> > subdirectory cannot exist without its parent and you cannot delete the parent if
> > it is not empty. Correct me if I am wrong.
> 
> It is an elegant way: an inode can only be deleted when the link count
> is zero. The fastest way to figure that out for directories would be to
> let subdirs increase the parent link count: you just have look up the
> link count in the parent instead of going through all directory entries
> searching for possible subdirectories.

I don't get the point here. If there are not only subdirectories but other
entries as well, you can't remove the directory anyway ...

		Tomas