Re: very poor ext3 write performance on big filesystems?

From: Andi Kleen <andi@firstfloor.org>
To: Theodore Tso <tytso@mit.edu>, Andi Kleen <andi@firstfloor.org>,
	Tomasz Chmielewski <mangoo@wpkg.org>,
	LKML <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: very poor ext3 write performance on big filesystems?
Date: Mon, 18 Feb 2008 16:18:23 +0100	[thread overview]
Message-ID: <20080218151823.GA26622@one.firstfloor.org> (raw)
In-Reply-To: <20080218141640.GC12568@mit.edu>

On Mon, Feb 18, 2008 at 09:16:41AM -0500, Theodore Tso wrote:
> ext3 tries to keep inodes in the same block group as their containing
> directory.  If you have lots of hard links, obviously it can't really
> do that, especially since we don't have a good way at mkdir time to
> tell the filesystem, "Psst!  This is going to be a hard link clone of
> that directory over there, put it in the same block group".

Hmm, you think such a hint interface would be worth it?

> 
> > What has helped a bit was to recreate the file system with -O^dir_index
> > dir_index seems to cause more seeks.
> 
> Part of it may have simply been recreating the filesystem, not

Undoubtedly.

> necessarily removing the dir_index feature.  Dir_index speeds up
> individual lookups, but it slows down workloads that do a readdir

But only for large directories right? For kernel source like
directory sizes it seems to be a general loss.

-Andi