linux-ext4 - Re: delalloc is crippling fs

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Message-ID: <4884B7CF.7060800@redhat.com>
Date:	Mon, 21 Jul 2008 11:22:39 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: delalloc is crippling fs_mark performance

Eric Sandeen wrote:
> running fs_mark like this:
> 
> fs_mark -d /mnt/test -D 256 -n 100000 -t 4 -s 20480 -F -S 0
> 
> (256 subdirs, 100000 files/iteration, 4 threads, 20k files, no sync)
> 
> on a 1T fs, with and without delalloc (mount option), is pretty interesting:
> 
> http://people.redhat.com/esandeen/ext4/fs_mark.png

I've updated this graph with another run where the group_prealloc
tuneable was set to a perfect multiple of the allocation size, or 500
blocks.  This way the leftover 2-block preallocations don't wind up
causing the list to grow with unuseable tiny leftover preallocations.
After tuning this way, it does clearly seem to be the problem here.

-Eric

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