linux-ext4 - Re: [PATCH 19/26] ext4: Defer clearing of PageWriteback after extent conversion

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Message-ID: <20130604182437.GJ3030@thunk.org>
Date:	Tue, 4 Jun 2013 14:24:37 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 19/26] ext4: Defer clearing of PageWriteback after extent
 conversion

On Fri, May 31, 2013 at 11:42:52AM +0200, Jan Kara wrote:
> Currently PageWriteback bit gets cleared from put_io_page() called from
> ext4_end_bio(). This is somewhat inconvenient as extent tree is not
> fully updated at that time (unwritten extents are not marked as written)
> so we cannot read the data back yet. This design was dictated by lock
> ordering as we cannot start a transaction while PageWriteback bit is set
> (we could easily deadlock with ext4_da_writepages()). But now that we
> use transaction reservation for extent conversion, locking issues are
> solved and we can move PageWriteback bit clearing after extent
> conversion is done. As a result we can remove wait for unwritt en extent
> conversion from ext4_sync_file() because it already implicitely happe ns
> through wait_on_page_writeback().
> 
> We implement deferring of PageWriteback clearing by queueing completed
> bios to appropriate io_end and processing all the pages when io_end is
> going to be freed instead of at the moment ext4_io_end() is called.
> 
> Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.

						- Ted
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