Re: [PATCH 2/6] writeback: the kupdate expire timestamp should bea moving target

[Mel Gorman]

On Thu, Jul 22, 2010 at 01:09:30PM +0800, Wu Fengguang wrote:
> Dynamicly compute the dirty expire timestamp at queue_io() time.
> Also remove writeback_control.older_than_this which is no longer used.
> 
> writeback_control.older_than_this used to be determined at entrance to
> the kupdate writeback work. This _static_ timestamp may go stale if the
> kupdate work runs on and on. The flusher may then stuck with some old
> busy inodes, never considering newly expired inodes thereafter.
> 
> This has two possible problems:
> 
> - It is unfair for a large dirty inode to delay (for a long time) the
>   writeback of small dirty inodes.
> 
> - As time goes by, the large and busy dirty inode may contain only
>   _freshly_ dirtied pages. Ignoring newly expired dirty inodes risks
>   delaying the expired dirty pages to the end of LRU lists, triggering
>   the very bad pageout(). Neverthless this patch merely addresses part
>   of the problem.
> 
> CC: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>

Again, makes sense and I can't see a problem. There are some worth
smithing issues in the changelog such as Dynamicly -> Dynamically and
s/writeback_control.older_than_this used/writeback_control.older_than_this is used/
but other than that.

Acked-by: Mel Gorman <mel@xxxxxxxxx>

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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