linux-kernel - Re: question on readahead and sync mounting

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Message-ID: <x497hq34ztn.fsf@segfault.boston.devel.redhat.com>
Date:	Tue, 23 Feb 2010 12:38:44 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	GeunSik Lim <leemgs1@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: question on readahead and sync mounting

Oliver Neukum <oliver@...kum.org> writes:

> Am Dienstag, 23. Februar 2010 00:48:39 schrieben Sie:
>> Please, Refer to below articles to understand readahead essentially.
>> 
>> http://lwn.net/Articles/235164/ (On-demand readahead by corbet)
>> http://kernelnewbies.org/Linux_2_6_23#head-102af265937262a7a21766ae58fddc1a29a5d8d7(
>> On-demand read-ahead on Linux 2.6.23)
>
> OK, I am looking for a way to make sure read requests on a SCSI drive
> actually hit the bus after a certain event. Is there a way to do this without
> tossing away the whole cache?

I'm not sure I understand what you're asking, but it sounds like you
want to do an O_DIRECT read.  Open the file with O_DIRECT, then pass
a properly-aligned buffer to the read(2) call.

Cheers,
Jeff
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