Re: [PATCH 1/3] mm, vmscan: count accidental reclaimed pages failed to put into lru

[Minchan Kim <minchan@kernel.org>]

On Wed, Apr 10, 2013 at 02:48:22PM +0900, Joonsoo Kim wrote:
> Hello, Minchan.
> 
> On Tue, Apr 09, 2013 at 02:55:14PM +0900, Minchan Kim wrote:
> > Hello Joonsoo,
> > 
> > On Tue, Apr 09, 2013 at 10:21:16AM +0900, Joonsoo Kim wrote:
> > > In shrink_(in)active_list(), we can fail to put into lru, and these pages
> > > are reclaimed accidentally. Currently, these pages are not counted
> > > for sc->nr_reclaimed, but with this information, we can stop to reclaim
> > > earlier, so can reduce overhead of reclaim.
> > > 
> > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > 
> > Nice catch!
> > 
> > But this patch handles very corner case and makes reclaim function's name
> > rather stupid so I'd like to see text size change after we apply this patch.
> > Other nipicks below.
> 
> Ah... Yes.
> I can re-work it to add number to sc->nr_reclaimed directly for both cases,
> shrink_active_list() and age_active_anon().

Sounds better.

> 
> > 
> > > 
> > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > > index 0f615eb..5d60ae0 100644
> > > --- a/include/linux/gfp.h
> > > +++ b/include/linux/gfp.h
> > > @@ -365,7 +365,7 @@ void *alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask);
> > >  extern void __free_pages(struct page *page, unsigned int order);
> > >  extern void free_pages(unsigned long addr, unsigned int order);
> > >  extern void free_hot_cold_page(struct page *page, int cold);
> > > -extern void free_hot_cold_page_list(struct list_head *list, int cold);
> > > +extern unsigned long free_hot_cold_page_list(struct list_head *list, int cold);
> > >  
> > >  extern void __free_memcg_kmem_pages(struct page *page, unsigned int order);
> > >  extern void free_memcg_kmem_pages(unsigned long addr, unsigned int order);
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 8fcced7..a5f3952 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1360,14 +1360,18 @@ out:
> > >  /*
> > >   * Free a list of 0-order pages
> > >   */
> > > -void free_hot_cold_page_list(struct list_head *list, int cold)
> > > +unsigned long free_hot_cold_page_list(struct list_head *list, int cold)
> > >  {
> > > +	unsigned long nr_reclaimed = 0;
> > 
> > How about nr_free or nr_freed for consistent with function title?
> 
> Okay.
> 
> > 
> > >  	struct page *page, *next;
> > >  
> > >  	list_for_each_entry_safe(page, next, list, lru) {
> > >  		trace_mm_page_free_batched(page, cold);
> > >  		free_hot_cold_page(page, cold);
> > > +		nr_reclaimed++;
> > >  	}
> > > +
> > > +	return nr_reclaimed;
> > >  }
> > >  
> > >  /*
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index 88c5fed..eff2927 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -915,7 +915,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> > >  		 */
> > >  		__clear_page_locked(page);
> > >  free_it:
> > > -		nr_reclaimed++;
> > >  
> > >  		/*
> > >  		 * Is there need to periodically free_page_list? It would
> > > @@ -954,7 +953,7 @@ keep:
> > >  	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
> > >  		zone_set_flag(zone, ZONE_CONGESTED);
> > >  
> > > -	free_hot_cold_page_list(&free_pages, 1);
> > > +	nr_reclaimed += free_hot_cold_page_list(&free_pages, 1);
> > 
> > Nice cleanup.
> > 
> > >  
> > >  	list_splice(&ret_pages, page_list);
> > >  	count_vm_events(PGACTIVATE, pgactivate);
> > > @@ -1321,7 +1320,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> > >  	if (nr_taken == 0)
> > >  		return 0;
> > >  
> > > -	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
> > > +	nr_reclaimed += shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
> > >  					&nr_dirty, &nr_writeback, false);
> > 
> > Do you have any reason to change?
> > To me, '=' is more clear to initialize the variable.
> > When I see above, I have to look through above lines to catch where code
> > used the nr_reclaimed.
> > 
> 
> There is no reason, I will change it.
> 
> > >  
> > >  	spin_lock_irq(&zone->lru_lock);
> > > @@ -1343,7 +1342,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> > >  
> > >  	spin_unlock_irq(&zone->lru_lock);
> > >  
> > > -	free_hot_cold_page_list(&page_list, 1);
> > > +	nr_reclaimed += free_hot_cold_page_list(&page_list, 1);
> > 
> > How about considering vmstat, too?
> > It could be minor but you are considering freed page as
> > reclaim context. (ie, sc->nr_reclaimed) so it would be more appropriate.
> 
> I don't understand what you mean.
> Please explain more what you have in mind :)

We are accouting PGSTEAL_[KSWAPD|DIRECT] with nr_reclaimed and
nr_reclaimed are contributing for sc->nr_reclaimed accumulation but
your patch doesn't consider that so vmstat cound be not exact.
Of course, it's not exact inherently so no big deal that's why I said "minor".
I just want that you think over about that.

Thanks!

> 
> > 
> > >  
> > >  	/*
> > >  	 * If reclaim is isolating dirty pages under writeback, it implies
> > > @@ -1438,7 +1437,7 @@ static void move_active_pages_to_lru(struct lruvec *lruvec,
> > >  		__count_vm_events(PGDEACTIVATE, pgmoved);
> > >  }
> > >  
> > > -static void shrink_active_list(unsigned long nr_to_scan,
> > > +static unsigned long shrink_active_list(unsigned long nr_to_scan,
> > >  			       struct lruvec *lruvec,
> > >  			       struct scan_control *sc,
> > >  			       enum lru_list lru)
> > > @@ -1534,7 +1533,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
> > >  	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
> > >  	spin_unlock_irq(&zone->lru_lock);
> > >  
> > > -	free_hot_cold_page_list(&l_hold, 1);
> > > +	return free_hot_cold_page_list(&l_hold, 1);
> > 
> > It would be better to add comment about return value.
> > Otherwise, people could confuse with the number of pages moved from
> > active to inactive.
> > 
> 
> In next spin, I will not change return type.
> So above problem will be disappreared.
> 
> > >  }
> > >  
> > >  #ifdef CONFIG_SWAP
> > > @@ -1617,7 +1616,8 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
> > >  {
> > >  	if (is_active_lru(lru)) {
> > >  		if (inactive_list_is_low(lruvec, lru))
> > > -			shrink_active_list(nr_to_scan, lruvec, sc, lru);
> > > +			return shrink_active_list(nr_to_scan, lruvec, sc, lru);
> > > +
> > 
> > Unnecessary change.
> > 
> 
> Why?

You are adding unnecessary newline.

> 
> > >  		return 0;
> > >  	}
> > >  
> > > @@ -1861,8 +1861,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> > >  	 * rebalance the anon lru active/inactive ratio.
> > >  	 */
> > >  	if (inactive_anon_is_low(lruvec))
> > > -		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
> > > -				   sc, LRU_ACTIVE_ANON);
> > > +		sc->nr_reclaimed += shrink_active_list(SWAP_CLUSTER_MAX,
> > > +					lruvec, sc, LRU_ACTIVE_ANON);
> > >  
> > >  	throttle_vm_writeout(sc->gfp_mask);
> > >  }
> > > @@ -2470,23 +2470,27 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> > >  }
> > >  #endif
> > >  
> > > -static void age_active_anon(struct zone *zone, struct scan_control *sc)
> > 
> > Comment about return value.
> > or rename but I have no idea. Sorry.
> 
> This will be disappreared in next spin.
> 
> Thanks for detailed review.
> 
> > 
> > > +static unsigned long age_active_anon(struct zone *zone,
> > > +					struct scan_control *sc)
> > >  {
> > > +	unsigned long nr_reclaimed = 0;
> > >  	struct mem_cgroup *memcg;
> > >  
> > >  	if (!total_swap_pages)
> > > -		return;
> > > +		return 0;
> > >  
> > >  	memcg = mem_cgroup_iter(NULL, NULL, NULL);
> > >  	do {
> > >  		struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
> > >  
> > >  		if (inactive_anon_is_low(lruvec))
> > > -			shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
> > > -					   sc, LRU_ACTIVE_ANON);
> > > +			nr_reclaimed += shrink_active_list(SWAP_CLUSTER_MAX,
> > > +					lruvec, sc, LRU_ACTIVE_ANON);
> > >  
> > >  		memcg = mem_cgroup_iter(NULL, memcg, NULL);
> > >  	} while (memcg);
> > > +
> > > +	return nr_reclaimed;
> > >  }
> > >  
> > >  static bool zone_balanced(struct zone *zone, int order,
> > > @@ -2666,7 +2670,7 @@ loop_again:
> > >  			 * Do some background aging of the anon list, to give
> > >  			 * pages a chance to be referenced before reclaiming.
> > >  			 */
> > > -			age_active_anon(zone, &sc);
> > > +			sc.nr_reclaimed += age_active_anon(zone, &sc);
> > >  
> > >  			/*
> > >  			 * If the number of buffer_heads in the machine
> > > -- 
> > > 1.7.9.5
> > > 
> > > --
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> > 
> > -- 
> > Kind regards,
> > Minchan Kim
> > 
> > --
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-- 
Kind regards,
Minchan Kim

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