linux-kernel - Re: [PATCH v5 8/8] mm: add vmstat counters for tracking PCP drains

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Date:	Tue, 03 Jan 2012 12:47:48 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
CC:	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v5 8/8] mm: add vmstat counters for tracking PCP drains

(1/2/12 5:24 AM), Gilad Ben-Yossef wrote:
> This patch introduces two new vmstat counters: pcp_global_drain
> that counts the number of times a per-cpu pages global drain was
> requested and pcp_global_ipi_saved that counts the number of times
> the number of CPUs with per-cpu pages in any zone were less then
> 1/2 of the number of online CPUs.
> 
> The patch purpose is to show the usefulness of only sending an IPI
> asking to drain per-cpu pages to CPUs that actually have them
> instead of a blind global IPI. It is probably not useful by itself.
> 
> Signed-off-by: Gilad Ben-Yossef<gilad@...yossef.com>
> CC: Christoph Lameter<cl@...ux.com>
> CC: Chris Metcalf<cmetcalf@...era.com>
> CC: Peter Zijlstra<a.p.zijlstra@...llo.nl>
> CC: Frederic Weisbecker<fweisbec@...il.com>
> CC: linux-mm@...ck.org
> CC: Pekka Enberg<penberg@...nel.org>
> CC: Matt Mackall<mpm@...enic.com>
> CC: Sasha Levin<levinsasha928@...il.com>
> CC: Rik van Riel<riel@...hat.com>
> CC: Andi Kleen<andi@...stfloor.org>
> CC: Mel Gorman<mel@....ul.ie>
> CC: Andrew Morton<akpm@...ux-foundation.org>
> CC: Alexander Viro<viro@...iv.linux.org.uk>
> CC: Avi Kivity<avi@...hat.com>
> ---
>   include/linux/vm_event_item.h |    1 +
>   mm/page_alloc.c               |    4 ++++
>   mm/vmstat.c                   |    2 ++
>   3 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index 03b90cd..3657f6f 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -58,6 +58,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>   		THP_COLLAPSE_ALLOC_FAILED,
>   		THP_SPLIT,
>   #endif
> +		PCP_GLOBAL_DRAIN, PCP_GLOBAL_IPI_SAVED,
>   		NR_VM_EVENT_ITEMS
>   };
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 092c331..4ca6bfa 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1140,6 +1140,10 @@ void drain_all_pages(void)
>   				cpumask_clear_cpu(cpu, cpus_with_pcps);
>   		}
>   	on_each_cpu_mask(cpus_with_pcps, drain_local_pages, NULL, 1);
> +
> +	count_vm_event(PCP_GLOBAL_DRAIN);
> +	if (cpumask_weight(cpus_with_pcps)<  (cpumask_weight(cpu_online_mask) / 2))
> +		count_vm_event(PCP_GLOBAL_IPI_SAVED);

NAK.

PCP_GLOBAL_IPI_SAVED is only useful at development phase. I can't
imagine normal admins use it.



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