linux-ext4 - Re: [PATCH 15/26] ext4: Restructure writeback path

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Date:	Tue, 4 Jun 2013 13:18:24 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 15/26] ext4: Restructure writeback path

On Fri, May 31, 2013 at 11:42:48AM +0200, Jan Kara wrote:
> There are two issues with current writeback path in ext4. For one we
> don't necessarily map complete pages when blocksize < pagesize and thus
> needn't do any writeback in one iteration. We always map some blocks
> though so we will eventually finish mapping the page. Just if writeback
> races with other operations on the file, forward progress is not really
> guaranteed. The second problem is that current code structure makes it
> hard to associate all the bios to some range of pages with one io_end
> structure so that unwritten extents can be converted after all the bios
> are finished. This will be especially difficult later when io_end will
> be associated with reserved transaction handle.
> 
> We restructure the writeback path to a relatively simple loop which
> first prepares extent of pages, then maps one or more extents so that
> no page is partially mapped, and once page is fully mapped it is
> submitted for IO. We keep all the mapping and IO submission information
> in mpage_da_data structure to somewhat reduce stack usage. Resulting
> code is somewhat shorter than the old one and hopefully also easier to
> read.
> 
> Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.

					- Ted
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