linux-ext4 - Re: bio splits unnecessarily due to BH

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Date:	Thu, 21 Mar 2013 17:43:52 +0900
From:	Kazuya Mio <k-mio@...jp.nec.com>
To:	Jan Kara <jack@...e.cz>
CC:	akpm@...ux-foundation.org, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org
Subject: Re: bio splits unnecessarily due to BH_Boundary in ext3 direct I/O

2013/03/20 4:31, Jan Kara wrote:
>   I'm not sure I understand. Looking into dio_send_cur_page() it seems may
> prematurely submit the bio if sdio->boundary is set - in that case we
> should probably first try to add the page to the bio and submit the bio
> only after that. Is that what you mean?

I think the direct I/O works for each page into buffer_head by the following
three steps:
1. submit sdio->bio if sdio->boudary is set
2. add sdio->cur_page to sdio->bio by dio_new_bio() or dio_bio_add_page()
3. set the curret page to sdio->cur_page in submit_page_section()

It is true that dio_send_cur_page() submits the bio if sdio->boudary is set.
However, at this time, this bio does not contain sdio->cur_page and
the current page do_direct_IO() passed.

Regards,
Kazuya Mio

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