linux-kernel - Re: [PATCH 14/40] autonuma: add page structure fields

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Message-ID: <4FEDEE9F.4080103@redhat.com>
Date:	Fri, 29 Jun 2012 14:06:23 -0400
From:	Rik van Riel <riel@...hat.com>
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>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 14/40] autonuma: add page structure fields

On 06/28/2012 08:55 AM, Andrea Arcangeli wrote:
> On 64bit archs, 20 bytes are used for async memory migration (specific
> to the knuma_migrated per-node threads), and 4 bytes are used for the
> thread NUMA false sharing detection logic.
>
> This is a bad implementation due lack of time to do a proper one.

It is not ideal, no.

If you document what everything does, maybe somebody else
will understand the code well enough to help fix it.

> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -136,6 +136,32 @@ 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.
> +	 */

Once you fix it, could you fold the fix into this patch?

> +	/*
> +	 * To modify autonuma_last_nid lockless the architecture,
> +	 * needs SMP atomic granularity<  sizeof(long), not all archs
> +	 * have that, notably some ancient alpha (but none of those
> +	 * should run in NUMA systems). 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

Please document what these fields mean.


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