Re: [patch 04/11] mm: memcg: push down PageSwapCache check intouncharge entry functions

[Johannes Weiner]

On Mon, Jul 09, 2012 at 11:42:12AM +0900, Kamezawa Hiroyuki wrote:
> (2012/07/05 9:44), Johannes Weiner wrote:
> > @@ -3278,10 +3283,11 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
> >   		unused = oldpage;
> >   	}
> >   	anon = PageAnon(used);
> > -	__mem_cgroup_uncharge_common(unused,
> > -		anon ? MEM_CGROUP_CHARGE_TYPE_ANON
> > -		     : MEM_CGROUP_CHARGE_TYPE_CACHE,
> > -		true);
> > +	if (!PageSwapCache(page))
> > +		__mem_cgroup_uncharge_common(unused,
> > +					     anon ? MEM_CGROUP_CHARGE_TYPE_ANON
> > +					     : MEM_CGROUP_CHARGE_TYPE_CACHE,
> > +					     true);
> 
> !PageSwapCache(unused) ?

Argh, right.

> But I think unused page's PG_swapcache is always dropped. So, the check is
> not necessary.

Oh, this is intentional: the check was in __mem_cgroup_uncharge_common
before, which means it applied to this entry point as well.  This is
supposed to be a mechanical change that does not change any logic.
The check is then removed in the next patch.

---
Subject: mm: memcg: push down PageSwapCache check into uncharge entry functions fix

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a3bf414..f4ff18a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3283,7 +3283,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
 		unused = oldpage;
 	}
 	anon = PageAnon(used);
-	if (!PageSwapCache(page))
+	if (!PageSwapCache(unused))
 		__mem_cgroup_uncharge_common(unused,
 					     anon ? MEM_CGROUP_CHARGE_TYPE_ANON
 					     : MEM_CGROUP_CHARGE_TYPE_CACHE,

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