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

From: Daniel Phillips (
Date: Wed Feb 21 2001 - 22:43:07 EST

"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.

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This archive was generated by hypermail 2b29 : Fri Feb 23 2001 - 21:00:26 EST