linux-kernel - Re: [PATCH v7 2/2] mm: make lru_add_drain

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Message-ID: <20130813235104.GK28996@mtj.dyndns.org>
Date:	Tue, 13 Aug 2013 19:51:04 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: Re: [PATCH v7 2/2] mm: make lru_add_drain_all() selective

On Tue, Aug 13, 2013 at 07:44:55PM -0400, Chris Metcalf wrote:
> int lru_add_drain_all(void)
> {
>         static struct cpumask mask;

Instead of cpumask,

>         static DEFINE_MUTEX(lock);

you can DEFINE_PER_CPU(struct work_struct, ...).

>         for_each_online_cpu(cpu) {
>                 if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
>                     pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||
>                     pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
>                     need_activate_page_drain(cpu))
>                         cpumask_set_cpu(cpu, &mask);

and schedule the work items directly.

>         }
> 
>         rc = schedule_on_cpu_mask(lru_add_drain_per_cpu, &mask);

Open coding flushing can be a bit bothersome but you can create a
per-cpu workqueue and schedule work items on it and then flush the
workqueue instead too.

No matter how flushing is implemented, the path wouldn't have any
memory allocation, which I thought was the topic of the thread, no?

Thanks.

-- 
tejun
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