linux-kernel - Re: [cpuops cmpxchg V2 4/5] vmstat: User per cpu atomics to avoid interrupt disable / enable

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Message-ID: <alpine.DEB.2.00.1012151056280.13049@router.home>
Date:	Wed, 15 Dec 2010 11:01:27 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Tejun Heo <tj@...nel.org>
cc:	akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops cmpxchg V2 4/5] vmstat: User per cpu atomics to avoid
 interrupt disable / enable

On Wed, 15 Dec 2010, Tejun Heo wrote:

> +		/*
> +		 * The fetching of the stat_threshold is racy. We may apply
> +		 * a counter threshold to the wrong the cpu if we get
> +		 * rescheduled while executing here. However, the following
> +		 * will apply the threshold again and therefore bring the
> +		 * counter under the threshold.
> +		 */
>
> What does "the following" mean here?  Later executions of the
> function?  It seems like the counter can go out of the threshold at
> least temporarily, which probably is okay but I think the comment can
> be improved a bit.

I meant later execution of the function. I will fix the comment.

Subject: vmstat comment fix

Clarify comments for the threshold a bit.

Signed-off-by: Christoh Lameter <cl@...ux.com>

---
 mm/vmstat.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Index: linux-2.6/mm/vmstat.c
===================================================================
--- linux-2.6.orig/mm/vmstat.c	2010-12-15 10:57:44.000000000 -0600
+++ linux-2.6/mm/vmstat.c	2010-12-15 10:58:46.000000000 -0600
@@ -277,9 +277,12 @@ static inline void mod_state(struct zone
 		/*
 		 * The fetching of the stat_threshold is racy. We may apply
 		 * a counter threshold to the wrong the cpu if we get
-		 * rescheduled while executing here. However, the following
-		 * will apply the threshold again and therefore bring the
-		 * counter under the threshold.
+		 * rescheduled while executing here. However, the next
+		 * counter update will apply the threshold again and
+		 * therefore bring the counter under the threshold again.
+		 *
+		 * Most of the time the thresholds are the same anyways
+		 * for all cpus in a zone.
 		 */
 		t = this_cpu_read(pcp->stat_threshold);

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