linux-ext4 - Re: bigalloc and max file size

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Message-Id: <A0C1821A-B597-4617-BD14-B638143DC3C2@mit.edu>
Date:	Mon, 31 Oct 2011 06:15:23 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Tao Ma <tm@....ma>
Cc:	Theodore Tso <tytso@....edu>,
	Andreas Dilger <adilger@...mcloud.com>,
	linux-ext4 development <linux-ext4@...r.kernel.org>,
	Alex Zhuravlev <bzzz@...mcloud.com>,
	"hao.bigrat@...il.com" <hao.bigrat@...il.com>
Subject: Re: bigalloc and max file size

On Oct 27, 2011, at 11:31 PM, Tao Ma wrote:

> Forget to say, if we increase the extent length to be cluster, there are
> also a good side effect. ;) Current bigalloc has a severe performance
> regression in the following test case:
> mount -t ext4 /dev/sdb1 /mnt/ext4
> cp linux-3.0.tar.gz /mnt/ext4
> cd /mnt/ext4
> tar zxvf linux-3.0.tar.gz
> umount /mnt/ext4

I've been traveling, so I haven't had a chance to test this, but it makes no sense that changing the encoding fro the extent length would change the performance of the forced writeback caused by amount.   There may be a performance bug that we should fix, or may have been fixed by accident with the extent encoding change. 

Have you investigated why this got better when you changed the meaning of the extent length field?   It makes no sense that such a format change would have such an impact….

-- Ted

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