linux-kernel - Re: [PATCH 3/4] mm: move lazy free pages to inactive list

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Date:	Tue, 31 Mar 2015 14:57:29 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Shaohua Li <shli@...nel.org>, Yalin.Wang@...ymobile.com
Subject: Re: [PATCH 3/4] mm: move lazy free pages to inactive list

On Mon, Mar 30, 2015 at 10:28:47PM -0700, Andrew Morton wrote:
> On Tue, 31 Mar 2015 13:45:25 +0900 Minchan Kim <minchan@...nel.org> wrote:
> > > 
> > > deactivate_page() doesn't look at or alter PageReferenced().  Should it?
> > 
> > Absolutely true. Thanks.
> > Here it goes.
> > 
> > >From 2b2c92eb73a1cceac615b9abd4c0f5f0c3395ff5 Mon Sep 17 00:00:00 2001
> > From: Minchan Kim <minchan@...nel.org>
> > Date: Tue, 31 Mar 2015 13:38:46 +0900
> > Subject: [PATCH] mm: lru_deactivate_fn should clear PG_referenced
> > 
> > deactivate_page aims for accelerate for reclaiming through
> > moving pages from active list to inactive list so we should
> > clear PG_referenced for the goal.
> > 
> > ...
> >
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -800,6 +800,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
> >  
> >  		del_page_from_lru_list(page, lruvec, lru + LRU_ACTIVE);
> >  		ClearPageActive(page);
> > +		ClearPageReferenced(page);
> >  		add_page_to_lru_list(page, lruvec, lru);
> >  
> >  		__count_vm_event(PGDEACTIVATE);
> 
> What if we have
> 
> 	PageLRU(page) && !PageActive(page) && PageReferenced(page)
> 
> if we really want to "accelerate the reclaim of @page" then we should
> clear PG_referenced there too.

The function's name is *deactivate*_page. IOW, I think it should work
for only pages in active list, IMHO.

> 
> (And what about page_referenced(page) :))

Yes, I considered it when you mentioned PG_referenced. Now, madvise_free
clear out access bit of page table when the syscall is called so
shrink_page_list could reclaim pages easily.

Of course, we could clear access bit by page_referenced for general purpose,
not only madvise_free but it would hurt performance for madvise_free so
I'd like to leave it unless there is a need for the function.

-- 
Kind regards,
Minchan Kim
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