linux-ext4 - Re: [PATCH] ext4: Don't allow lg prealloc list to be grow large.

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Date:	Mon, 21 Jul 2008 14:37:19 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC:	cmm@...ibm.com, tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Don't allow lg prealloc list to be grow large.

Aneesh Kumar K.V wrote:
> The locality group prealloc list is freed only when there is a block allocation
> failure. This can result in large number of per cpu locality group prealloc space
> and also make the ext4_mb_use_preallocated expensive. Add a tunable max_lg_prealloc
> which default to 1000. If we have more than 1000 Per-CPU prealloc space and if we
> fail to find a suitable prealloc space during allocation we will now free all
> the prealloc space in the locality group.

It looks like this helps, but does not fare as well as the "perfectly
tuned" default (where the prealloc size is a multiple of the 20k/5 block
file size used in the test.)

I've added a plot of a delalloc run with your patch to the graph at:

http://people.redhat.com/esandeen/ext4/fs_mark.png

-Eric


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