linux-ext4 - Re: [PATCH 0/3] Ext3 latency improvement patches

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Date:	Fri, 27 Mar 2009 20:14:04 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Theodore Tso <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Chris Mason <chris.mason@...cle.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 0/3] Ext3 latency improvement patches

Theodore Tso wrote:
> OTOH, the really big databases will tend to use direct I/O, so they
> won't be dirtying the page cache anyway.  So maybe it's not worth the

Not necessarily...  From what I understand, a lot of the individual 
low-level components in cloud storage, such as GoogleFS's chunk 
server[1] do not bypass the page cache, even though they do care about 
the details of data caching and data consistency.

I am looking at the same areas for my own distributed storage work, and 
am finding that the current crop of Linux-specific, 
database/server-friendly syscalls permit more application control over 
pagecache usage than in past years, decreasing the need for O_DIRECT. 
Things like readahead(2), sync_file_range(2), fadvise(3), really help.

	Jeff

[1] http://labs.google.com/papers/gfs-sosp2003.pdf

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