linux-kernel - Re: [PATCH] [RT] avoid preemption in memory controller code

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Message-ID: <alpine.DEB.1.10.0812081138470.26257@gandalf.stny.rr.com>
Date:	Mon, 8 Dec 2008 11:42:06 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tim Blechmann <tim@...ngt.org>
cc:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] [RT] avoid preemption in memory controller code


Hi Tim,

On Mon, 8 Dec 2008, Tim Blechmann wrote:

> the lru_lock of struct mem_group_per_zone is used to avoid preemption
> during the __mem_cgroup_stat_add_safe function.
> therefore, a raw_spinlock_t should be used.

What is the reason that this must avoid preemption? Is there another
way to solve this? I rather not just add a raw spinlock if we can
help it.

-- Steve

> 
> Signed-off-by: Tim Blechmann <tim@...ngt.org>
> ---
>  mm/memcontrol.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 517f945..8661732 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -95,9 +95,9 @@ enum mem_cgroup_zstat_index {
>  
>  struct mem_cgroup_per_zone {
>  	/*
> -	 * spin_lock to protect the per cgroup LRU
> +	 * raw_spin_lock to protect the per cgroup LRU
>  	 */
> -	spinlock_t		lru_lock;
> +	raw_spinlock_t		lru_lock;
>  	struct list_head	active_list;
>  	struct list_head	inactive_list;
>  	unsigned long count[NR_MEM_CGROUP_ZSTAT];
> -- 
> 1.5.6.3
> 
> 
> 
--
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