linux-kernel - Re: [PATCH v8 7/8] mm: only IPI CPUs to drain local pages if they exist

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Date:	Wed, 08 Feb 2012 10:33:13 +0100
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	linux-kernel@...r.kernel.org,
	"Gilad Ben-Yossef" <gilad@...yossef.com>
Cc:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>,
	"Chris Metcalf" <cmetcalf@...era.com>,
	"Frederic Weisbecker" <fweisbec@...il.com>,
	"Russell King" <linux@....linux.org.uk>, 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>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Alexander Viro" <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, "Avi Kivity" <avi@...hat.com>,
	"Milton Miller" <miltonm@....com>
Subject: Re: [PATCH v8 7/8] mm: only IPI CPUs to drain local pages if they
 exist

On Sun, 05 Feb 2012 14:48:41 +0100, Gilad Ben-Yossef <gilad@...yossef.com> wrote:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d2186ec..3ff5aff 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1161,11 +1161,46 @@ void drain_local_pages(void *arg)
>  }
> /*
> - * Spill all the per-cpu pages from all CPUs back into the buddy allocator
> + * Spill all the per-cpu pages from all CPUs back into the buddy allocator.
> + *
> + * Note that this code is protected against sending an IPI to an offline
> + * CPU but does not guarantee sending an IPI to newly hotplugged CPUs:
> + * on_each_cpu_mask() blocks hotplug and won't talk to offlined CPUs but
> + * nothing keeps CPUs from showing up after we populated the cpumask and
> + * before the call to on_each_cpu_mask().
>   */
>  void drain_all_pages(void)
>  {
> -	on_each_cpu(drain_local_pages, NULL, 1);
> +	int cpu;
> +	struct per_cpu_pageset *pcp;
> +	struct zone *zone;
> +
> +	/* Allocate in the BSS so we wont require allocation in
> +	 * direct reclaim path for CONFIG_CPUMASK_OFFSTACK=y
> +	 */

If you are going to send next iteration, this comment should have
“/*” on its own line just like comment below.

> +	static cpumask_t cpus_with_pcps;
> +
> +	/*
> +	 * We don't care about racing with CPU hotplug event
> +	 * as offline notification will cause the notified
> +	 * cpu to drain that CPU pcps and on_each_cpu_mask
> +	 * disables preemption as part of its processing
> +	 */
> +	for_each_online_cpu(cpu) {
> +		bool has_pcps = false;
> +		for_each_populated_zone(zone) {
> +			pcp = per_cpu_ptr(zone->pageset, cpu);
> +			if (pcp->pcp.count) {
> +				has_pcps = true;
> +				break;
> +			}
> +		}
> +		if (has_pcps)
> +			cpumask_set_cpu(cpu, &cpus_with_pcps);
> +		else
> +			cpumask_clear_cpu(cpu, &cpus_with_pcps);
> +	}
> +	on_each_cpu_mask(&cpus_with_pcps, drain_local_pages, NULL, 1);
>  }
> #ifdef CONFIG_HIBERNATION


-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--
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