linux-kernel - Re: [PATCH 0/3] ramzswap: Eliminate stale data in compressed memory

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Date:	Wed, 05 May 2010 21:35:17 +0530
From:	Nitin Gupta <ngupta@...are.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Greg KH <greg@...ah.com>, Minchan Kim <minchan.kim@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Cyp <cyp561@...il.com>, driverdev <devel@...verdev.osuosl.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] ramzswap: Eliminate stale data in compressed memory

On 05/05/2010 08:44 PM, Linus Torvalds wrote:
> 
> 
> On Wed, 5 May 2010, Nitin Gupta wrote:
>>
>> ramzswap driver creates RAM based block devices which can be
>> used (only) as swap disks. Pages swapped to these disks are
>> compressed and stored in memory itself.
> 
> Ok, this patch series looks way better, if only because it looks less 
> hacky.
> 
> That said, I absolutely _hate_ the f*cking notifier model that takes 
> "type" flags. It's a disgrace. It's a horrible horrible model.
> 

You mean you didn't like the 'swap type' value passed around by notifier
calls, as here:
 "blocking_notifier_call_chain(&swapon_notify_list, type, swap_file);" ?

> I'd much rather bind a nice "swap_operations" structure to the device, and 
> have that structure have function pointers for the different operations. 
> No stupid "operation type codes". Real, honest-to-goodness function 
> pointers.
> 

I think such 'swap_operations' structure will be have to be part of
block_device_operations, so we may access it from swap_entry_free()
where a swap slot is freed. This will also get rid of all this notifier
stuff.

The patch you nacked did something similar: it add 'swap_slot_free_callback'
directly to block_device_operations. Without such change, I could not think
of any way to do away with notifiers.


> The notifier layer is a total piece of sh*t. I'm sorry I ever merged it, 
> and I'm _doubly_ sorry that it's use is so horribly widespread. It's a 
> mistake.

Thanks,
Nitin
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