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Date: Fri, 14 Feb 2014 14:17:05 +0100
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Nicholas Mc Guire <der.herr@hofr.at>
Cc: linux-rt-users@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>, Carsten Emde <C.Emde@osadl.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andreas Platschek <platschek@ict.tuwien.ac.at>
Subject: Re: [PATCH RT 4/5] allow preemption in
 mem_cgroup_move_account_page_stat
Message-ID: <20140214131705.GF28438@linutronix.de>
References: <20140210153933.GE20017@opentech.at>
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* Nicholas Mc Guire | 2014-02-10 16:39:33 [+0100]:

>index a67e630f..e7cc35a 100644
>--- a/mm/memcontrol.c
>+++ b/mm/memcontrol.c
>@@ -3784,10 +3784,10 @@ void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
> 					enum mem_cgroup_stat_index idx)
> {
> 	/* Update stat data for mem_cgroup */
>-	preempt_disable();
>+	migrate_disable();
> 	__this_cpu_sub(from->stat->count[idx], nr_pages);
> 	__this_cpu_add(to->stat->count[idx], nr_pages);
>-	preempt_enable();
>+	migrate_enable();
> }

Now, that I look at it again. Isn't it more efficient to keep preemption
disabled for this very short time instead instead of invoking
migrate_disable() which includes preempt_disable()/enable() and a few
more opcodes…
Therefore, I drop it again.

Sebastian