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Date: Wed, 10 Apr 2013 15:03:53 +0900
From: Minchan Kim <minchan@...nel.org>
To: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 1/3] mm, vmscan: count accidental reclaimed pages failed
to put into lru
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@....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
> > >
> > > --
> > > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > > the body to majordomo@...ck.org. For more info on Linux MM,
> > > see: http://www.linux-mm.org/ .
> > > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> >
> > --
> > Kind regards,
> > Minchan Kim
> >
> > --
> > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > the body to majordomo@...ck.org. For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
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>
> --
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> see: http://www.linux-mm.org/ .
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--
Kind regards,
Minchan Kim
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