linux-kernel - Re: Question regarding concurrent accesses through block device and fs

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Message-ID: <m2ab85nw28.fsf@gmail.com>
Date:	Sun, 01 Mar 2009 15:42:55 +0100
From:	Francis Moreau <francis.moro@...il.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Question regarding concurrent accesses through block device and fs

[ 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@...oo.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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