linux-kernel - Re: [PATCH 04/10] Use percpu buffers

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Message-ID: <AANLkTin7_fKxTzE2rngh1Ew5Ss8F_Aw0s9Gz6ySug6SX@mail.gmail.com>
Date:	Mon, 9 Aug 2010 21:57:42 +0300
From:	Pekka Enberg <penberg@...nel.org>
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@...uxdriverproject.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] Use percpu buffers

On Mon, Aug 9, 2010 at 8:26 PM, Nitin Gupta <ngupta@...are.org> wrote:
> @@ -303,38 +307,41 @@ static int zram_write(struct zram *zram, struct bio *bio)
>                                zram_test_flag(zram, index, ZRAM_ZERO))
>                        zram_free_page(zram, index);
>
> -               mutex_lock(&zram->lock);
> +               preempt_disable();
> +               zbuffer = __get_cpu_var(compress_buffer);
> +               zworkmem = __get_cpu_var(compress_workmem);
> +               if (unlikely(!zbuffer || !zworkmem)) {
> +                       preempt_enable();
> +                       goto out;
> +               }

The per-CPU buffer thing with this preempt_disable() trickery looks
overkill to me. Most block device drivers seem to use mempool_alloc()
for this sort of thing. Is there some reason you can't use that here?
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