linux-kernel - Re: readahead on directories

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Message-ID: <4BCF123C.6010400@cfl.rr.com>
Date:	Wed, 21 Apr 2010 10:57:00 -0400
From:	Phillip Susi <psusi@....rr.com>
To:	Jamie Lokier <jamie@...reable.org>
CC:	linux-fsdevel@...r.kernel.org,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: readahead on directories

On 4/20/2010 8:44 PM, Jamie Lokier wrote:
> readahead() doesn't make much sense on a directory - the offset and
> size aren't meaningful.
> 
> But does plain opendir/readdir/closedir solve the problem?

No, since those are synchronous.  I want to have readahead() queue up
reading the entire directory in the background to avoid blocking, and
get the queue filled with a bunch of requests that can be merged into
larger segments before being dispatched to the hardware.

I don't actually care to have the contents of the directories returned,
so readdir() does more than I need in that respect, and also it performs
a blocking read of one disk block at a time, which is horribly slow with
a cold cache.
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