linux-ext4 - Re: HUGE slowdown when doing dpkg with ext4 over nbd

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Date:   Wed, 7 Dec 2016 10:52:48 +0100 (CET)
From:   Renaud Mariana <rmariana@...ine.net>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: HUGE slowdown when doing dpkg with ext4 over nbd

Here are my answers, hope it will help solve this issue, thanks.

Recap:
dpkg kibana on ext4 over a nbd device takes 10 minutes 
with xfs it's only 30s.
with ext4 no extends only 30s.

kernels :
4.5.7 has this issue as older kernel like 4.4.34 
The issue is also when nbd client & server run on same host 

How small are the files?
here is the histogram of file sizes : http://pasteboard.co/6HC3nKyk2.png
We can see 5000 files around 512 Bytes.

dpkg using fallocate() ?
Yes, there are 16044 calls by the same process
what are these uninitialized extents ?

Cheers, Renaud
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