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SubjectRe: [patch rfc] memcg: remove NULL check from lookup_page_cgroup() result
On Thu, 3 Feb 2011 15:12:30 +0100
Johannes Weiner <hannes@cmpxchg.org> wrote:

> The page_cgroup array is set up before even fork is initialized. I
> seriously doubt that this code executes before the array is alloc'd.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

I don't have solid answer to this. If some module use radix-tree and enter pages
to it, mem_cgroup may see it. But..

For my opinion, tring this is good.

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

> ---
> mm/memcontrol.c | 5 +----
> 1 files changed, 1 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a145c9e..6abaa10 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2343,10 +2343,7 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
> }
>
> pc = lookup_page_cgroup(page);
> - /* can happen at boot */
> - if (unlikely(!pc))
> - return 0;
> - prefetchw(pc);
> + BUG_ON(!pc); /* XXX: remove this and move pc lookup into commit */
>
> ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, oom, page_size);
> if (ret || !mem)
> --
> 1.7.4
>



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