linux-ext4 - Re: [RFC] ext4: Don't send extra barrier during fsync if there are no dirty pages.

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Message-ID: <x49pqxwc1p3.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 05 Aug 2010 15:13:44 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	Avi Kivity <avi@...hat.com>, Christoph Hellwig <hch@...radead.org>,
	Ric Wheeler <rwheeler@...hat.com>,
	Mingming Cao <cmm@...ibm.com>, djwong@...ibm.com,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Keith Mannthey <kmannth@...ibm.com>,
	Mingming Cao <mcao@...ibm.com>
Subject: Re: [RFC] ext4: Don't send extra barrier during fsync if there are no dirty pages.

"Ted Ts'o" <tytso@....edu> writes:

> On Thu, Aug 05, 2010 at 05:20:12AM +0300, Avi Kivity wrote:
>> 
>> Why not?  To be clear, I'm talking about an io_submit() with
>> multiple IO_CMD_FSYNC requests, with a kernel implementation that is
>> able to batch these requests.
>
> IO_CMD_FSYNC doesn't exist right now, but sure, it means we don't have

Well, there's IOCB_CMD_FSYNC.  But still, this isn't the same thing as
what's requested.  If I understand correctly, what is requested is a
mechanism to flush out all data for multiple file descriptors and follow
that with a single barrier/flush (and yes, Ted did give a summary of the
commands that would be required to accomplish that).

There still remains the question of why this should be tied to the AIO
submission interface.


Cheers,
Jeff
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