linux-kernel - Re: [PATCH 03/10] Use percpu stats

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Date:	Mon, 30 Aug 2010 11:20:10 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Nitin Gupta <ngupta@...are.org>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Linux Driver Project <devel@...verdev.osuosl.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/10] Use percpu stats

On Mon, 9 Aug 2010, Nitin Gupta wrote:

> -static void zram_stat_inc(u32 *v)
> +static void zram_add_stat(struct zram *zram,
> +			enum zram_stats_index idx, s64 val)
>  {
> -	*v = *v + 1;
> +	struct zram_stats_cpu *stats;
> +
> +	preempt_disable();
> +	stats = __this_cpu_ptr(zram->stats);
> +	u64_stats_update_begin(&stats->syncp);
> +	stats->count[idx] += val;
> +	u64_stats_update_end(&stats->syncp);
> +	preempt_enable();

Maybe do

#define zram_add_stat(zram, index, val)
		this_cpu_add(zram->stats->count[index], val)

instead? It creates an add in a single "atomic" per cpu instruction and
deals with the fallback scenarios for processors that cannot handle 64
bit adds.

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