Re: [rfc] Near-constant time directory index for Ext2

["H. Peter Anvin" <hpa@transmeta.com>]

Daniel Phillips wrote:
> 
> "H. Peter Anvin" wrote:
> >
> > Andreas Dilger wrote:
> > >
> > > Basically (IMHO) we will not really get any noticable benefit with 1 level
> > > index blocks for a 1k filesystem - my estimates at least are that the break
> > > even point is about 5k files.  We _should_ be OK with 780k files in a single
> > > directory for a while.
> > >
> >
> > I've had a news server with 2000000 files in one directory.  Such a
> > filesystem is likely to use small blocks, too, because each file is
> > generally small.
> >
> > This is an important connection: filesystems which have lots and lots of
> > small files will have large directories and small block sizes.
> 
> I mentioned this earlier but it's worth repeating: the desire to use a
> small block size is purely an artifact of the fact that ext2 has no
> handling for tail block fragmentation.  That's a temporary situation -
> once we've dealt with it your 2,000,000 file directory will be happier
> with 4K filesystem blocks.  There will be a lot fewer metadata index
> blocks in your directory file, for one thing.  Another practical matter
> is that 4K filesystem blocks map directly to 4K PAGE_SIZE and are as a
> result friendlier to the page cache and memory manager.
> 

Well, that's something I really don't expect to see anymore -- this
"purely temporary situation" is now already 7 years old at least.

	-hpa

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