linux-kernel - Re: [PATCH 1/2] [mmotm] Add notifiers for various swap events

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Date:	Mon, 28 Dec 2009 15:51:31 +0530
From:	Nitin Gupta <ngupta@...are.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] [mmotm] Add notifiers for various swap events

On Mon, Dec 28, 2009 at 11:43 AM, Pekka Enberg <penberg@...helsinki.fi> wrote:
> On Mon, Dec 28, 2009 at 3:19 AM, Nitin Gupta <ngupta@...are.org> wrote:
>> Events:
>>  - Swapon
>>  - Swapoff
>>  - When a swap slot is freed

<snip>

> This looks good to me. Hugh? Nitin, does this patch cause any
> performance hit for the !CONFIG_RAMZSWAP case?
>

I have not yet collected any data to check overhead in !RAMZSWAP
case but an empty notifier chain is essentially equivalent to:

rcu_read_lock()
        nb = rcu_dereference(*nl);
rcu_read_unlock()

This should not cause any performance problem. Anyway, I will
try to come up with some numbers to confirm this.

Thanks for looking into this.
Nitin
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