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SubjectRe: [PATCH] pagemap: fix wrong KPF_THP on slab pages
On Tue, Sep 25, 2012 at 1:05 PM, Naoya Horiguchi
<n-horiguchi@ah.jp.nec.com> wrote:
> On Tue, Sep 25, 2012 at 11:59:51AM -0400, KOSAKI Motohiro wrote:
>> On Tue, Sep 25, 2012 at 9:56 AM, Naoya Horiguchi
>> <n-horiguchi@ah.jp.nec.com> wrote:
>> > KPF_THP can be set on non-huge compound pages like slab pages, because
>> > PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug
>> > and breaks user space applications which look for thp via /proc/kpageflags.
>> > Currently thp is constructed only on anonymous pages, so this patch makes
>> > KPF_THP be set when both of PageAnon and PageTransCompound are true.
>>
>> Indeed. Please add some comment too.
>
> Sure. I send revised one.
>
> Thanks,
> Naoya
> ---
> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Date: Mon, 24 Sep 2012 16:28:30 -0400
> Subject: [PATCH v2] pagemap: fix wrong KPF_THP on slab pages
>
> KPF_THP can be set on non-huge compound pages like slab pages, because
> PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug
> and breaks user space applications which look for thp via /proc/kpageflags.
> Currently thp is constructed only on anonymous pages, so this patch makes
> KPF_THP be set when both of PageAnon and PageTransCompound are true.
>
> Changelog in v2:
> - add a comment in code
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> ---
> fs/proc/page.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index 7fcd0d6..f7cd2f6c 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -115,7 +115,12 @@ u64 stable_page_flags(struct page *page)
> u |= 1 << KPF_COMPOUND_TAIL;
> if (PageHuge(page))
> u |= 1 << KPF_HUGE;
> - else if (PageTransCompound(page))
> + /*
> + * Since THP is relevant only for anonymous pages so far, we check it
> + * explicitly with PageAnon. Otherwise thp is confounded with non-huge
> + * compound pages like slab pages.
> + */
> + else if (PageTransCompound(page) && PageAnon(page))
> u |= 1 << KPF_THP;

Looks good to me.

Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>


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