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SubjectRe: [patch 5/8] mm: memcg: remove unneeded checks from newpage_charge()
On Thu, Nov 24, 2011 at 09:04:43AM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 23 Nov 2011 16:42:28 +0100
> Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> > From: Johannes Weiner <jweiner@redhat.com>
> >
> > All callsites pass in freshly allocated pages and a valid mm. As a
> > result, all checks pertaining the page's mapcount, page->mapping or
> > the fallback to init_mm are unneeded.
> >
> > Signed-off-by: Johannes Weiner <jweiner@redhat.com>
>
> Hmm, it's true now. But for making clear our assumption to all readers of code,
>
> could you add
> VM_BUG_ON(!mm || page_mapped(page) || (page->mapping && !PageAnon(page)) ?

Of course. Please find the delta patch below. I broke them up into
three separate checks to make the problem easier to find if the BUG
triggers.

> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Thank you.

---
From: Johannes Weiner <jweiner@redhat.com>
Subject: mm: memcg: remove unneeded checks from newpage_charge() fix
Document page state assumptions and catch if they are violated in
newpage_charge().

Signed-off-by: Johannes Weiner <jweiner@redhat.com>
---
mm/memcontrol.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0d10be4..f338018 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2679,6 +2679,9 @@ int mem_cgroup_newpage_charge(struct page *page,
{
if (mem_cgroup_disabled())
return 0;
+ VM_BUG_ON(page_mapped(page));
+ VM_BUG_ON(page->mapping && !PageAnon(page));
+ VM_BUG_ON(!mm);
return mem_cgroup_charge_common(page, mm, gfp_mask,
MEM_CGROUP_CHARGE_TYPE_MAPPED);
}
--
1.7.6.4

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