linux-kernel - Re: [PATCH 13/35] autonuma: add page structure fields

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Date:	Tue, 29 May 2012 15:16:25 +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 13/35] autonuma: add page structure fields

On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:

> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 780ded7..e8dc82c 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -126,6 +126,31 @@ struct page {
>  		struct page *first_page;	/* Compound tail pages */
>  	};
>  
> +#ifdef CONFIG_AUTONUMA
> +	/*
> +	 * FIXME: move to pgdat section along with the memcg and allocate
> +	 * at runtime only in presence of a numa system.
> +	 */
> +	/*
> +	 * To modify autonuma_last_nid lockless the architecture,
> +	 * needs SMP atomic granularity < sizeof(long), not all archs
> +	 * have that, notably some alpha. Archs without that requires
> +	 * autonuma_last_nid to be a long.
> +	 */
> +#if BITS_PER_LONG > 32
> +	int autonuma_migrate_nid;
> +	int autonuma_last_nid;
> +#else
> +#if MAX_NUMNODES >= 32768
> +#error "too many nodes"
> +#endif
> +	/* FIXME: remember to check the updates are atomic */
> +	short autonuma_migrate_nid;
> +	short autonuma_last_nid;
> +#endif
> +	struct list_head autonuma_migrate_node;
> +#endif
> +
>  	/*
>  	 * On machines where all RAM is mapped into kernel address space,
>  	 * we can simply calculate the virtual address. On machines with


24 bytes per page.. or ~0.6% of memory gone. This is far too great a
price to pay.

At LSF/MM Rik already suggested you limit the number of pages that can
be migrated concurrently and use this to move the extra list_head out of
struct page and into a smaller amount of extra structures, reducing the
total overhead.


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