linux-ext4 - Re: Bug#605009: serious performance regression with ext4

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Message-ID: <82oc98f63j.fsf@mid.bfk.de>
Date:	Mon, 29 Nov 2010 16:27:12 +0000
From:	Florian Weimer <fweimer@....de>
To:	Bernd Schubert <bernd.schubert@...tmail.fm>
Cc:	"Ted Ts'o" <tytso@....edu>, Jonathan Nieder <jrnieder@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: Bug#605009: serious performance regression with ext4

* Bernd Schubert:

> Wouldn't it make sense to modify ext4 or even the vfs to do that on close() 
> itself? Most applications expect the file to be on disk after a close anyway 
> and I also don't see a good reason why one should delay a disk write-back 
> after close any longer (well, there are exeption if the application is broken, 
> for example such as ha-logd used by pacemaker, which did for each line of logs 
> an open, seek, write, flush, close sequence..., but at least we have fixed 
> that in -hg now).

If you use Oracle Berkeley DB in a process-based fashion, it is
crucial for decent performance that the memory-mapped file containing
the cache is not flushed to disk when the database environment is
closed prior to process termination.  Perhaps flushing could be
delayed until the last open file handle is gone.  In any case, it's a
pretty drastic change, which should probably be tunable with a
(generic) mount option.

-- 
Florian Weimer                <fweimer@....de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99
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