linux-kernel - Re: O_NONBLOCK with Ext3

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Date:	Sat, 12 Jun 2010 12:37:02 +0530
From:	"Yedire, Sandeep" <syedire@...il.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: O_NONBLOCK with Ext3

On 12 June 2010 00:26, Jeff Moyer <jmoyer@...hat.com> wrote:
> "Yedire, Sandeep" <syedire@...il.com> writes:
>
>> Hi ALL,
>> I am currently using o_nonblock flag for writing a file of 64MB over a
>> flash device. Flash is formatted with ext3 filesystem with default
>> options.
>> When instrumented the driver code for collecting the erase/write count
>> at sector level. I noticed that o_nonblock has no effect on this
>> count. There is no difference in erase/write count with o_nonblock
>> flag or without this flag.
>> When selected Ext2 as filesystem I noticed a significant difference in
>> the erase/write count.
>> There were more updates with o_nonblock and test application was
>> faster. I could confirm this by checking the Dirty page limit in the
>> background. It was updating faster in case of Ext2 not incase of Ext3.
>>
>> Can any one explain on o_nonblock flag in case of  Ext3 filesystem?
>
> The O_NONBLOCK flag should be ignored when opening files on a file
> system.  I'm not sure how to explain your observations.
>
> What exactly were you trying to accomplish?
>
> Cheers,
> Jeff
>
--
[Sandeep]
> What exactly were you trying to accomplish?
>
I am only trying to observe the difference with O_NONBLOCK flag in the
updates to filesystem blocks and data blocks in Ext2 and Ext3
filesystem.

It was observed that with O_NONBLOCK flag in Ext2 there were less
updates to Filesystem block at sector 0, and frequent updates to data
blocks. This is not the case with Ext3.

Sandeep
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