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

[Erik Mouw <erik@harddisk-recovery.com>]

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.


Erik

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