From mboxrd@z Thu Jan  1 00:00:00 1970
From: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
Subject: Re: [PATCH] btrfs: call mark_inode_dirty when i_size is updated
Date: Tue, 03 Feb 2009 09:36:23 +0900
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 <1233583946.18113.6.camel@think.oraclecorp.com>
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Cc: linux-btrfs@vger.kernel.org
To: Chris Mason <chris.mason@oracle.com>
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At 23:12 09/02/02, Chris Mason wrote:
>On Mon, 2009-02-02 at 20:00 +0900, Hisashi Hifumi wrote:
>> Hi Chris.
>> 
>> I think it is needed to call mark_inode_dirty() when file size expands
>> in order to flush metadata updates to HDD through sync() syscall or
>> background_writeout().
>> 
>
>Thanks for reading through this code and sending the patch.
>
>I find the I_DIRTY flags one of the more confusing parts of the generic
>fs writeback cdoe.  But, I think what happens is the
>btrfs_set_page_dirty function calls __set_page_dirty_nobuffers() which
>does:
>
>if (mapping->host) {
>     /* !PageAnon && !swapper_space */
>      __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
>}
>
>This should be enough to make sure the btrfs inodes are processed by
>background writeout and sync().  Please let me know if I'm misreading
>things.

Surely, as you pointed out, btrfs_set_page_dirty calls
if (mapping->host) {
     /* !PageAnon && !swapper_space */
      __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
}
through _set_page_dirty_nobuffers.
But I_DIRTY_PAGES is not sufficient.
To flush metadata update to HDD through sync(), I_DIRTY_SYNC or 
I_DIRTY_DATASYNC flag is needed. see __sync_single_inode.

Thanks.