Re: [PATCH 2/3] Reclaim invalidated page ASAP

[Mel Gorman <mel@csn.ul.ie>]

On Tue, Nov 30, 2010 at 10:10:20AM +0900, KOSAKI Motohiro wrote:
> > invalidate_mapping_pages is very big hint to reclaimer.
> > It means user doesn't want to use the page any more.
> > So in order to prevent working set page eviction, this patch
> > move the page into tail of inactive list by PG_reclaim.
> > 
> > Please, remember that pages in inactive list are working set
> > as well as active list. If we don't move pages into inactive list's
> > tail, pages near by tail of inactive list can be evicted although
> > we have a big clue about useless pages. It's totally bad.
> > 
> > Now PG_readahead/PG_reclaim is shared.
> > fe3cba17 added ClearPageReclaim into clear_page_dirty_for_io for
> > preventing fast reclaiming readahead marker page.
> > 
> > In this series, PG_reclaim is used by invalidated page, too.
> > If VM find the page is invalidated and it's dirty, it sets PG_reclaim
> > to reclaim asap. Then, when the dirty page will be writeback,
> > clear_page_dirty_for_io will clear PG_reclaim unconditionally.
> > It disturbs this serie's goal.
> > 
> > I think it's okay to clear PG_readahead when the page is dirty, not
> > writeback time. So this patch moves ClearPageReadahead.
> > 
> > Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
> > Acked-by: Rik van Riel <riel@redhat.com>
> > Cc: Wu Fengguang <fengguang.wu@intel.com>
> > Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Nick Piggin <npiggin@kernel.dk>
> > Cc: Mel Gorman <mel@csn.ul.ie>
> 
> I still dislike this one. I doubt this trick makes much benefit in real
> world workload.
> 

I would agree except as said elsewhere, it's a chicken and egg problem.
We don't have a real world test because fadvise is not useful in its
current iteration. I'm hoping that there will be a test comparing

rsync		on vanilla kernel
rsync		on patched kernel
rsync+patch	on vanilla kernel
rsync+patch	on patched kernel

Are the results of such a test likely to happen?

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

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