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SubjectRe: [patch 5/8] mm: memcg: remove unneeded checks from newpage_charge()
On Thu 24-11-11 10:04:09, Johannes Weiner wrote:
> 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.

sounds reasonable.

>
> > 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>

I assume you are going to fold it into the previous one.
Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
> 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

--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic


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