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SubjectRe: [patch 5/8] mm: memcg: remove unneeded checks from newpage_charge()
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)) ?

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

> ---
> mm/memcontrol.c | 13 +------------
> 1 files changed, 1 insertions(+), 12 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d4d139a..0d10be4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2679,19 +2679,8 @@ int mem_cgroup_newpage_charge(struct page *page,
> {
> if (mem_cgroup_disabled())
> return 0;
> - /*
> - * If already mapped, we don't have to account.
> - * If page cache, page->mapping has address_space.
> - * But page->mapping may have out-of-use anon_vma pointer,
> - * detecit it by PageAnon() check. newly-mapped-anon's page->mapping
> - * is NULL.
> - */
> - if (page_mapped(page) || (page->mapping && !PageAnon(page)))
> - return 0;
> - if (unlikely(!mm))
> - mm = &init_mm;
> return mem_cgroup_charge_common(page, mm, gfp_mask,
> - MEM_CGROUP_CHARGE_TYPE_MAPPED);
> + MEM_CGROUP_CHARGE_TYPE_MAPPED);
> }
>
> static void
> --
> 1.7.6.4
>
> --
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