linux-kernel - Re: [PATCH v3] UDF: Add support for O

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Message-ID: <50471558.4030505@mev.co.uk>
Date:	Wed, 5 Sep 2012 10:03:20 +0100
From:	Ian Abbott <abbotti@....co.uk>
To:	Jan Kara <jack@...e.cz>
CC:	Ian Abbott <ian.abbott@....co.uk>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v3] UDF: Add support for O_DIRECT

On 2012-09-04 16:11, Ian Abbott wrote:
> On 2012-09-04 15:39, Jan Kara wrote:
>> On Tue 04-09-12 10:49:39, Ian Abbott wrote:
>>> Add support for the O_DIRECT flag.  There are two cases to deal with:
>>    Out of curiosity, do you have a use for this feature or is it mostly
>> academic interest?
>
> I'm planning to use it for an embedded project that needs to stream
> large files off a CompactFlash card, but the data doesn't need to be in
> the buffer cache as its only read once, and the system has very limited
> memory bandwidth so I can't afford the the extra copy.  The old version
> of this project only supported FAT, but that limited the file size to
> about 4GiB.  The filesystem needs to be something reasonably
> Windows-friendly, at least for adding the files to the CompactFlash card
> in the first place.

Actually, remembering back (the old project was about 3 years ago), the 
main reason for using O_DIRECT was it was causing too much memory 
fragmentation on my MMU-less embedded system.  That and the extra 
overhead of managing the buffer cache for data that was only read once.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-
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