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

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Date:	Tue, 30 Nov 2010 09:18:22 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ben Gamari <bgamari.foss@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH 2/3] Reclaim invalidated page ASAP

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@...il.com>
> > Acked-by: Rik van Riel <riel@...hat.com>
> > Cc: Wu Fengguang <fengguang.wu@...el.com>
> > Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > Cc: Johannes Weiner <hannes@...xchg.org>
> > Cc: Nick Piggin <npiggin@...nel.dk>
> > Cc: Mel Gorman <mel@....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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