linux-kernel - Re: Question about synchronous write on SSD

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Message-ID: <20080219091608.1da174c1@crazy>
Date:	Tue, 19 Feb 2008 09:16:08 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	"Kyungmin Park" <kmpark@...radead.org>
Cc:	"Linux Filesystem Mailing List" <linux-fsdevel@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: Question about synchronous write on SSD

Hi,

Le Tue, 19 Feb 2008 14:48:18 +0900,
"Kyungmin Park" <kmpark@...radead.org> a écrit :

> +               /* Write synchronous */
> +               bio->bi_rw |= (1 << BIO_RW_SYNC);

Adding BIO_RW_SYNC doesn't make generic_make_request() synchronous as
in "generic_make_request() returns only after write completion".
BIO_RW_SYNC only asks the I/O layer to unplug immediatly. But
generic_make_request() still returns before the completion of the I/O,
and the completion is notified asynchronously.

See:
 http://lxr.free-electrons.com/source/include/linux/bio.h#139

Sincerly,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Free Embedded Linux Training Materials
on http://free-electrons.com/training
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