linux-kernel - Re: [PATCH 09/10] vmscan: Setup pagevec as late as possible in shrink_page

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Date:	Fri, 16 Apr 2010 15:34:29 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Chris Mason <chris.mason@...cle.com>,
	Dave Chinner <david@...morbit.com>,
	Andi Kleen <andi@...stfloor.org>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 09/10] vmscan: Setup pagevec as late as possible in
	shrink_page_list()

On Fri, Apr 16, 2010 at 04:54:03PM +0900, KOSAKI Motohiro wrote:
> > shrink_page_list() sets up a pagevec to release pages as according as they
> > are free. It uses significant amounts of stack on the pagevec. This
> > patch adds pages to be freed via pagevec to a linked list which is then
> > freed en-masse at the end. This avoids using stack in the main path that
> > potentially calls writepage().
> > 
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > ---
> >  mm/vmscan.c |   34 ++++++++++++++++++++++++++--------
> >  1 files changed, 26 insertions(+), 8 deletions(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 9bc1ede..2c22c83 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -619,6 +619,22 @@ static enum page_references page_check_references(struct page *page,
> >  	return PAGEREF_RECLAIM;
> >  }
> >  
> > +static void free_page_list(struct list_head *free_list)
> > +{
> > +	struct pagevec freed_pvec;
> > +	struct page *page, *tmp;
> > +
> > +	pagevec_init(&freed_pvec, 1);
> > +
> > +	list_for_each_entry_safe(page, tmp, free_list, lru) {
> > +		list_del(&page->lru);
> > +		if (!pagevec_add(&freed_pvec, page)) {
> > +			__pagevec_free(&freed_pvec);
> > +			pagevec_reinit(&freed_pvec);
> > +		}
> > +	}
> 
> Need this two line at this? because we need consider number of
> list element are not 14xN.
> 
> 	if (pagevec_count(&freed_pvec))
> 		__pagevec_free(&freed_pvec);
> 

Whoops, yes indeed. Otherwise this potentially leaks and as
SWAP_CLUSTER_MAX is 32, it's often not going to be 14xN

> 
> > +}
> > +
> >  /*
> >   * shrink_page_list() returns the number of reclaimed pages
> >   */
> > @@ -627,13 +643,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> >  					enum pageout_io sync_writeback)
> >  {
> >  	LIST_HEAD(ret_pages);
> > -	struct pagevec freed_pvec;
> > +	LIST_HEAD(free_list);
> >  	int pgactivate = 0;
> >  	unsigned long nr_reclaimed = 0;
> >  
> >  	cond_resched();
> >  
> > -	pagevec_init(&freed_pvec, 1);
> >  	while (!list_empty(page_list)) {
> >  		enum page_references references;
> >  		struct address_space *mapping;
> > @@ -808,10 +823,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> >  		__clear_page_locked(page);
> >  free_it:
> >  		nr_reclaimed++;
> > -		if (!pagevec_add(&freed_pvec, page)) {
> > -			__pagevec_free(&freed_pvec);
> > -			pagevec_reinit(&freed_pvec);
> > -		}
> > +
> > +		/*
> > +		 * Is there need to periodically free_page_list? It would
> > +		 * appear not as the counts should be low
> > +		 */
> > +		list_add(&page->lru, &free_list);
> >  		continue;
> >  
> >  cull_mlocked:
> > @@ -834,9 +851,10 @@ keep:
> >  		list_add(&page->lru, &ret_pages);
> >  		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
> >  	}
> > +
> > +	free_page_list(&free_list);
> > +
> >  	list_splice(&ret_pages, page_list);
> > -	if (pagevec_count(&freed_pvec))
> > -		__pagevec_free(&freed_pvec);
> >  	count_vm_events(PGACTIVATE, pgactivate);
> >  	return nr_reclaimed;
> >  }
> > -- 
> > 1.6.5
> > 
> 
> 
> 

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