linux-kernel - Re: [PATCH] vmscan: reclaim_clean_pages_from

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Date:	Tue, 4 Aug 2015 00:33:33 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Jaewon Kim <jaewon31.kim@...sung.com>
Cc:	akpm@...ux-foundation.org, mgorman@...e.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, jaewon31.kim@...il.com
Subject: Re: [PATCH] vmscan: reclaim_clean_pages_from_list() must count
 mlocked pages

On Mon, Aug 03, 2015 at 11:55:46PM +0900, Jaewon Kim wrote:
> 
> 
> On 2015년 08월 03일 21:27, Minchan Kim wrote:
> > Hello,
> > 
> > On Mon, Aug 03, 2015 at 07:18:27PM +0900, Jaewon Kim wrote:
> >> reclaim_clean_pages_from_list() decreases NR_ISOLATED_FILE by returned
> >> value from shrink_page_list(). But mlocked pages in the isolated
> >> clean_pages page list would be removed from the list but not counted as
> >> nr_reclaimed. Fix this miscounting by returning the number of mlocked
> >> pages and count it.
> > 
> > If there are pages not able to reclaim, VM try to migrate it and
> > have to handle the stat in migrate_pages.
> > If migrate_pages fails again, putback-fiends should handle it.
> > 
> > Is there anyting I am missing now?
> > 
> > Thanks.
> > 
> Hello
> 
> Only pages in cc->migratepages will be handled by migrate_pages or
> putback_movable_pages, and NR_ISOLATED_FILE will be counted properly.
> However mlocked pages will not be put back into cc->migratepages,
> and also not be counted in NR_ISOLATED_FILE because putback_lru_page
> in shrink_page_list does not increase NR_ISOLATED_FILE.
> The current reclaim_clean_pages_from_list assumes that shrink_page_list
> returns number of pages removed from the candidate list.
> 
> i.e)
> isolate_migratepages_range    : NR_ISOLATED_FILE += 10
> reclaim_clean_pages_from_list : NR_ISOLATED_FILE -= 5 (1 mlocked page)
> migrate_pages                 : NR_ISOLATED_FILE -=4
> => NR_ISOLATED_FILE increased by 1

Thanks for the clarity.

I think the problem is shrink_page_list is awkard. It put back to
unevictable pages instantly instead of passing it to caller while
it relies on caller for non-reclaimed-non-unevictable page's putback.

I think we can make it consistent so that shrink_page_list could
return non-reclaimed pages via page_list and caller can handle it.
As a bonus, it could try to migrate mlocked pages without retrial.

> 
> Thank you.
> >>
> >> Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
> >> ---
> >>  mm/vmscan.c | 10 ++++++++--
> >>  1 file changed, 8 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >> index 5e8eadd..5837695 100644
> >> --- a/mm/vmscan.c
> >> +++ b/mm/vmscan.c
> >> @@ -849,6 +849,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> >>  				      unsigned long *ret_nr_congested,
> >>  				      unsigned long *ret_nr_writeback,
> >>  				      unsigned long *ret_nr_immediate,
> >> +				      unsigned long *ret_nr_mlocked,
> >>  				      bool force_reclaim)
> >>  {
> >>  	LIST_HEAD(ret_pages);
> >> @@ -1158,6 +1159,7 @@ cull_mlocked:
> >>  			try_to_free_swap(page);
> >>  		unlock_page(page);
> >>  		putback_lru_page(page);
> >> +		(*ret_nr_mlocked)++;
> >>  		continue;
> >>  
> >>  activate_locked:
> >> @@ -1197,6 +1199,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
> >>  		.may_unmap = 1,
> >>  	};
> >>  	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
> >> +	unsigned long nr_mlocked = 0;
> >>  	struct page *page, *next;
> >>  	LIST_HEAD(clean_pages);
> >>  
> >> @@ -1210,8 +1213,10 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
> >>  
> >>  	ret = shrink_page_list(&clean_pages, zone, &sc,
> >>  			TTU_UNMAP|TTU_IGNORE_ACCESS,
> >> -			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
> >> +			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5,
> >> +			&nr_mlocked, true);
> >>  	list_splice(&clean_pages, page_list);
> >> +	ret += nr_mlocked;
> >>  	mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
> >>  	return ret;
> >>  }
> >> @@ -1523,6 +1528,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> >>  	unsigned long nr_unqueued_dirty = 0;
> >>  	unsigned long nr_writeback = 0;
> >>  	unsigned long nr_immediate = 0;
> >> +	unsigned long nr_mlocked = 0;
> >>  	isolate_mode_t isolate_mode = 0;
> >>  	int file = is_file_lru(lru);
> >>  	struct zone *zone = lruvec_zone(lruvec);
> >> @@ -1565,7 +1571,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> >>  
> >>  	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
> >>  				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
> >> -				&nr_writeback, &nr_immediate,
> >> +				&nr_writeback, &nr_immediate, &nr_mlocked,
> >>  				false);
> >>  
> >>  	spin_lock_irq(&zone->lru_lock);
> >> -- 
> >> 1.9.1
> >>
> > 

-- 
Kind regards,
Minchan Kim
--
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