linux-kernel - Re: [PATCH 1/2] [mmotm v2] Add notifiers for various swap events

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Message-ID: <4B3C68F7.60100@cs.helsinki.fi>
Date:	Thu, 31 Dec 2009 11:03:51 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Nitin Gupta <ngupta@...are.org>
CC:	Andi Kleen <andi@...stfloor.org>,
	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 v2] Add notifiers for various swap events

Nitin Gupta wrote:
> Events:
>  - Swapon
>  - Swapoff
>  - When a swap slot is freed
> 
> This is required for ramzswap module which implements RAM based block
> devices to be used as swap disks. These devices require a notification
> on these events to function properly.
> 
> Currently, I'm not sure if any of these event notifiers have any other
> users. However, adding ramzswap specific hooks instead of this generic
> approach resulted in a bad/hacky code with too many 'ifdef CONFIG_RAMZSWAP'
> spread all over the core kernel code.
> 
> For SWAP_EVENT_SLOT_FREE, callbacks are made under swap_lock. Currently, this
> is not a problem since ramzswap is the only user and the callback it registers
> can be safely made under this lock. However, if this event finds more users,
> we might have to work on reducing contention on this lock (per-swap lock?).
> 
> v2: added comment before swap slot free notifier call to clarify that
> ramzswap is currently the only user of this notifier.
> 
> Signed-off-by: Nitin Gupta <ngupta@...are.org>

Andi didn't seem to like this one and we're still waiting for Hugh to 
comment on the issue. But, FWIW,

Acked-by: Pekka Enberg <penberg@...helsinki.fi>

			Pekka
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