linux-kernel - Re: [PATCH 30/35] autonuma: reset autonuma page data when pages are freed

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Date:	Tue, 29 May 2012 18:30:29 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 30/35] autonuma: reset autonuma page data when pages are
 freed

On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:
> When pages are freed abort any pending migration. If knuma_migrated
> arrives first it will notice because get_page_unless_zero would fail.

But knuma_migrated can run on a different cpu than this free is
happening, ACCESS_ONCE() won't cure that.

What's that ACCESS_ONCE() good for?

Also, you already have an autonuma_ hook right there, why add more
#ifdeffery ?

> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> ---
>  mm/page_alloc.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3d1ee70..1d3163f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -614,6 +614,10 @@ static inline int free_pages_check(struct page *page)
>  		bad_page(page);
>  		return 1;
>  	}
> +	autonuma_migrate_page_remove(page);
> +#ifdef CONFIG_AUTONUMA
> +	ACCESS_ONCE(page->autonuma_last_nid) = -1;
> +#endif
>  	if (page->flags & PAGE_FLAGS_CHECK_AT_PREP)
>  		page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
>  	return 0;

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