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To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>
Subject: Re: Question regarding concurrent accesses through block device and fs
References: <m2hc2yulrw.fsf@gmail.com>
	<200902200044.48328.nickpiggin@yahoo.com.au>
	<38b2ab8a0902200610i6c91725cjc91adca31042daa9@mail.gmail.com>
	<200902231458.32911.nickpiggin@yahoo.com.au>
From: Francis Moreau <francis.moro@gmail.com>
Date: Sun, 01 Mar 2009 15:42:55 +0100
Message-ID: <m2ab85nw28.fsf@gmail.com>
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[ Sorry for being long to answer but I was off, I'm slow and there are
  a lot of complex code to dig out ! ]

Nick Piggin <nickpiggin@yahoo.com.au> writes:

> On Saturday 21 February 2009 01:10:24 Francis Moreau wrote:

[...]

>>   - looking at unmap_underlying_metadata(), there's no code to deal with
>>     meta data buffers. It gets the buffer and unmap it whatever the type of
>>     data it contains.
>
> That's why I say it only really works for buffer cache used by the same
> filesystem that is now known to be unused.
>

hum, I still don't know what you mean by this, sorry to be slow.


[...]

>> What am I missing ?
>
> That we might complete the write of the new buffer before the
> old buffer is finished writing out?

Ah yes actually I realize that I don't know where and when the inode
blocks are effectively written to the disk !

It seems that write_inode(), called after data are commited to the
disk, only marks the inode buffers as dirty but it performs no IO (at
least it looks so for ext2 when its 'do_sync' parameter is 0 which is
the case when this method is called by write_inode()).

Could you enlight me one more time ?

Thanks
-- 
Francis
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