Date:	Mon, 29 Nov 2010 15:49:54 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ben Gamari <bgamari.foss@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...nel.dk>, Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH v2 1/3] deactivate invalidated pages

On Sun, Nov 28, 2010 at 11:02:55PM +0800, Minchan Kim wrote:
> This patch is based on mmotm-11-23. 

I cannot find __pagevec_lru_deactive() in mmotm-11-23.
Do you have any more patches?

> Recently, there are reported problem about thrashing.
> (http://marc.info/?l=rsync&m=128885034930933&w=2)
> It happens by backup workloads(ex, nightly rsync).
> That's because the workload makes just use-once pages
> and touches pages twice. It promotes the page into
> active list so that it results in working set page eviction.
> 
> Some app developer want to support POSIX_FADV_NOREUSE.
> But other OSes don't support it, either.
> (http://marc.info/?l=linux-mm&m=128928979512086&w=2)
> 
> By Other approach, app developer uses POSIX_FADV_DONTNEED.
> But it has a problem. If kernel meets page is writing
> during invalidate_mapping_pages, it can't work.
> It is very hard for application programmer to use it.
> Because they always have to sync data before calling
> fadivse(..POSIX_FADV_DONTNEED) to make sure the pages could
> be discardable. At last, they can't use deferred write of kernel
> so that they could see performance loss.
> (http://insights.oetiker.ch/linux/fadvise.html)
> 
> In fact, invalidation is very big hint to reclaimer.
> It means we don't use the page any more. So let's move
> the writing page into inactive list's head.
> 
> Why I need the page to head, Dirty/Writeback page would be flushed
> sooner or later. This patch uses trick PG_reclaim so the page would
> be moved into tail of inactive list when the page writeout completes.
> 
> It can prevent writeout of pageout which is less effective than
> flusher's writeout.
> 
> This patch considers page_mappged(page) with working set.
> So the page could leave head of inactive to get a change to activate.
> 
> Originally, I reused lru_demote of Peter with some change so added
> his Signed-off-by.
> 
> Note :
> PG_reclaim trick of writeback page could race with end_page_writeback
> so this patch check PageWriteback one more. It makes race window time
> reall small. But by theoretical, it still have a race. But it's a trivial.
> 
> Quote from fe3cba17 and some modification
> "If some page PG_reclaim unintentionally, it will confuse readahead and
> make it restart the size rampup process. But it's a trivial problem, and
> can mostly be avoided by checking PageWriteback(page) first in readahead"
> 
> PG_reclaim trick of dirty page don't work now since clear_page_dirty_for_io
> always clears PG_reclaim. Next patch will fix it.
> 
> Reported-by: Ben Gamari <bgamari.foss@...il.com>
> Signed-off-by: Minchan Kim <minchan.kim@...il.com>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Cc: Wu Fengguang <fengguang.wu@...el.com>
> Cc: Rik van Riel <riel@...hat.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>
> 
> Changelog since v1:
>  - modify description
>  - correct typo
>  - add some comment
>  - change deactivation policy
> ---
>  mm/swap.c |   84 +++++++++++++++++++++++++++++++++++++++++++++---------------
>  1 files changed, 63 insertions(+), 21 deletions(-)
> 
> diff --git a/mm/swap.c b/mm/swap.c
> index 31f5ec4..345eca1 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -268,10 +268,65 @@ void add_page_to_unevictable_list(struct page *page)
>  	spin_unlock_irq(&zone->lru_lock);
>  }
>  
> -static void __pagevec_lru_deactive(struct pagevec *pvec)
> +/*
> + * This function is used by invalidate_mapping_pages.
> + * If the page can't be invalidated, this function moves the page
> + * into inative list's head or tail to reclaim ASAP and evict
> + * working set page.
> + *
> + * PG_reclaim means when the page's writeback completes, the page
> + * will move into tail of inactive for reclaiming ASAP.
> + *
> + * 1. active, mapped page -> inactive, head
> + * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
> + * 3. inactive, mapped page -> none
> + * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
> + * 5. others -> none
> + *
> + * In 4, why it moves inactive's head, the VM expects the page would
> + * be writeout by flusher. The flusher's writeout is much effective than
> + * reclaimer's random writeout.
> + */
> +static void __lru_deactivate(struct page *page, struct zone *zone)
>  {
> -	int i, lru, file;
> +	int lru, file;
> +	int active = 0;
> +
> +	if (!PageLRU(page))
> +		return;
> +
> +	if (PageActive(page))
> +		active = 1;
> +	/* Some processes are using the page */
> +	if (page_mapped(page) && !active)
> +		return;

It's good to check such protections if doing heuristic demotion.
However if requested explicitly by the user, I'm _much more_ inclined
to act stupid&dumb and meet the user's expectation. Or will this code
be called by someone other than DONTNEED? Sorry I have no context of
the full code.

> +	else if (PageWriteback(page)) {
> +		SetPageReclaim(page);
> +		/* Check race with end_page_writeback */
> +		if (!PageWriteback(page))
> +			ClearPageReclaim(page);

Does the double check help a lot?

> +	} else if (PageDirty(page))
> +		SetPageReclaim(page);

Typically there are much more dirty pages than writeback pages.
I guess it's a good place to call bdi_start_inode_writeback() which
was posted here: http://www.spinics.net/lists/linux-mm/msg10833.html

Thanks,
Fengguang

> +
> +	file = page_is_file_cache(page);
> +	lru = page_lru_base_type(page);
> +	del_page_from_lru_list(zone, page, lru + active);
> +	ClearPageActive(page);
> +	ClearPageReferenced(page);
> +	add_page_to_lru_list(zone, page, lru);
> +	if (active)
> +		__count_vm_event(PGDEACTIVATE);
> +
> +	update_page_reclaim_stat(zone, page, file, 0);
> +}
>  
> +/*
> + * This function must be called with preemption disable.
> + */
> +static void __pagevec_lru_deactivate(struct pagevec *pvec)
> +{
> +	int i;
>  	struct zone *zone = NULL;
>  
>  	for (i = 0; i < pagevec_count(pvec); i++) {
> @@ -284,21 +339,7 @@ static void __pagevec_lru_deactive(struct pagevec *pvec)
>  			zone = pagezone;
>  			spin_lock_irq(&zone->lru_lock);
>  		}
> -
> -		if (PageLRU(page)) {
> -			if (PageActive(page)) {
> -				file = page_is_file_cache(page);
> -				lru = page_lru_base_type(page);
> -				del_page_from_lru_list(zone, page,
> -						lru + LRU_ACTIVE);
> -				ClearPageActive(page);
> -				ClearPageReferenced(page);
> -				add_page_to_lru_list(zone, page, lru);
> -				__count_vm_event(PGDEACTIVATE);
> -
> -				update_page_reclaim_stat(zone, page, file, 0);
> -			}
> -		}
> +		__lru_deactivate(page, zone);
>  	}
>  	if (zone)
>  		spin_unlock_irq(&zone->lru_lock);
> @@ -336,11 +377,13 @@ static void drain_cpu_pagevecs(int cpu)
>  
>  	pvec = &per_cpu(lru_deactivate_pvecs, cpu);
>  	if (pagevec_count(pvec))
> -		__pagevec_lru_deactive(pvec);
> +		__pagevec_lru_deactivate(pvec);
>  }
>  
>  /*
> - * Forecfully demote a page to the tail of the inactive list.
> + * Forcefully deactivate a page.
> + * This function is used for reclaiming the page ASAP when the page
> + * can't be invalidated by Dirty/Writeback.
>   */
>  void lru_deactivate_page(struct page *page)
>  {
> @@ -348,12 +391,11 @@ void lru_deactivate_page(struct page *page)
>  		struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
>  
>  		if (!pagevec_add(pvec, page))
> -			__pagevec_lru_deactive(pvec);
> +			__pagevec_lru_deactivate(pvec);
>  		put_cpu_var(lru_deactivate_pvecs);
>  	}
>  }
>  
> -
>  void lru_add_drain(void)
>  {
>  	drain_cpu_pagevecs(get_cpu());
> -- 
> 1.7.0.4
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