Re: [patch 13/13] mm: memcontrol: rewrite uncharge API

[Johannes Weiner]

On Tue, Jul 15, 2014 at 06:07:35PM +0200, Michal Hocko wrote:
> On Tue 15-07-14 11:55:37, Naoya Horiguchi wrote:
> > On Wed, Jun 18, 2014 at 04:40:45PM -0400, Johannes Weiner wrote:
> > ...
> > > diff --git a/mm/swap.c b/mm/swap.c
> > > index a98f48626359..3074210f245d 100644
> > > --- a/mm/swap.c
> > > +++ b/mm/swap.c
> > > @@ -62,6 +62,7 @@ static void __page_cache_release(struct page *page)
> > >  		del_page_from_lru_list(page, lruvec, page_off_lru(page));
> > >  		spin_unlock_irqrestore(&zone->lru_lock, flags);
> > >  	}
> > > +	mem_cgroup_uncharge(page);
> > >  }
> > >  
> > >  static void __put_single_page(struct page *page)
> > 
> > This seems to cause a list breakage in hstate->hugepage_activelist
> > when freeing a hugetlbfs page.
> 
> This looks like a fall out from
> http://marc.info/?l=linux-mm&m=140475936311294&w=2
> 
> I didn't get to review this one but the easiest fix seems to be check
> HugePage and do not call uncharge.

Yes, that makes sense.  I'm also moving the uncharge call into
__put_single_page() and __put_compound_page() so that PageHuge(), a
function call, only needs to be checked for compound pages.

> > For hugetlbfs, we uncharge in free_huge_page() which is called after
> > __page_cache_release(), so I think that we don't have to uncharge here.
> > 
> > In my testing, moving mem_cgroup_uncharge() inside if (PageLRU) block
> > fixed the problem, so if that works for you, could you fold the change
> > into your patch?

Memcg pages that *do* need uncharging might not necessarily be on the
LRU list.

Does the following work for you?

Thanks!

---

diff --git a/mm/swap.c b/mm/swap.c
index 3461f2f5be20..af5c8ad830d1 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -62,12 +62,12 @@ static void __page_cache_release(struct page *page)
 		del_page_from_lru_list(page, lruvec, page_off_lru(page));
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	}
-	mem_cgroup_uncharge(page);
 }
 
 static void __put_single_page(struct page *page)
 {
 	__page_cache_release(page);
+	mem_cgroup_uncharge(page);
 	free_hot_cold_page(page, false);
 }
 
@@ -76,6 +76,8 @@ static void __put_compound_page(struct page *page)
 	compound_page_dtor *dtor;
 
 	__page_cache_release(page);
+	if (!PageHuge(page))
+		mem_cgroup_uncharge(page);
 	dtor = get_compound_page_dtor(page);
 	(*dtor)(page);
 }
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