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

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Message-ID: <20101130140333.GB1528@barrios-desktop>
Date:	Tue, 30 Nov 2010 23:03:33 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Mel Gorman <mel@....ul.ie>,
	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>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH 2/3] Reclaim invalidated page ASAP

On Tue, Nov 30, 2010 at 12:20:41PM +0100, Johannes Weiner wrote:
> On Tue, Nov 30, 2010 at 07:41:30AM +0900, Minchan Kim wrote:
> 
> > diff --git a/mm/swap.c b/mm/swap.c
> > index 19e0812..1f1f435 100644
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -275,28 +275,51 @@ void add_page_to_unevictable_list(struct page *page)
> >   * into inative list's head. Because the VM expects the page would
> >   * be writeout by flusher. The flusher's writeout is much effective
> >   * than reclaimer's random writeout.
> > + *
> > + * If the page isn't page_mapped and dirty/writeback, the page
> > + * could reclaim asap using PG_reclaim.
> > + *
> > + * 1. active, mapped page -> none
> > + * 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 lru, file;
> > -	unsigned long vm_flags;
> > +	int active = 0;
> 
> vm_flags is never used in this series.

It's garbage in my old version which is used page_referenced.

> 
> > -	if (!PageLRU(page) || !PageActive(page))
> > +	if (!PageLRU(page))
> >  		return;
> > -
> >  	/* Some processes are using the page */
> >  	if (page_mapped(page))
> >  		return;
> > -
> > -	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);
> > +	if (PageActive(page))
> > +		active = 1;
> 
> 	active = PageActive(page)

Will fix. 

> 
> > +	if (PageWriteback(page) || PageDirty(page)) {
> > +		/*
> > +		 * PG_reclaim could be raced with end_page_writeback
> > +		 * It can make readahead confusing.  But race window
> > +		 * is _really_ small and  it's non-critical problem.
> > +		 */
> > +		SetPageReclaim(page);
> > +
> > +		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);
> > +	}
> 
> If we lose the race with writeback, the completion handler won't see
> PG_reclaim, won't move the page, and we have an unwanted clean cache
> page on the active list.  Given the pagevec caching of those pages it
> could be rather likely that IO completes before the above executes.
> 
> Shouldn't this be
> 
> 	if (PageWriteback() || PageDirty()) {
> 		SetPageReclaim()
> 		move_to_inactive_head()
> 	} else {
> 		move_to_inactive_tail()
> 	}
> 
> instead?

Fair enough.

Thanks, Hannes.
> 
> 	Hannes

-- 
Kind regards,
Minchan Kim
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