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Message-ID: <4C60D9E6.3050700@vflare.org>
Date: Tue, 10 Aug 2010 10:17:34 +0530
From: Nitin Gupta <ngupta@...are.org>
To: Pekka Enberg <penberg@...nel.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 08/10/2010 12:27 AM, Pekka Enberg wrote:
> 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?
>
Other block drivers are allocating relatively small structs using
mempool_alloc(). However, in case of zram, these buffers are quite
large (compress_workmem is 64K!). So, allocating them on every write
would probably be much slower than using a pre-allocated per-cpu buffer.
Thanks,
Nitin
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