linux-kernel - Re: [PATCH] frontswap: enable call to invalidate area on swapoff

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Date:	Wed, 09 Oct 2013 15:50:13 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Krzysztof Kozlowski <k.kozlowski@...sung.com>, linux-mm@...ck.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, Shaohua Li <shli@...ionio.com>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH] frontswap: enable call to invalidate area on swapoff


On 10/09/2013 04:08 AM, Andrew Morton wrote:
> On Tue, 08 Oct 2013 10:13:20 +0200 Krzysztof Kozlowski <k.kozlowski@...sung.com> wrote:
> 
>> On pon, 2013-10-07 at 15:03 -0700, Andrew Morton wrote:
>>> On Mon, 07 Oct 2013 17:25:41 +0200 Krzysztof Kozlowski <k.kozlowski@...sung.com> wrote:
>>>
>>>> During swapoff the frontswap_map was NULL-ified before calling
>>>> frontswap_invalidate_area(). However the frontswap_invalidate_area()
>>>> exits early if frontswap_map is NULL. Invalidate was never called during
>>>> swapoff.
>>>>
>>>> This patch moves frontswap_map_set() in swapoff just after calling
>>>> frontswap_invalidate_area() so outside of locks
>>>> (swap_lock and swap_info_struct->lock). This shouldn't be a problem as
>>>> during swapon the frontswap_map_set() is called also outside of any
>>>> locks.
>>>>
>>>
>>> Ahem.  So there's a bunch of code in __frontswap_invalidate_area()
>>> which hasn't ever been executed and nobody noticed it.  So perhaps that
>>> code isn't actually needed?
>>>
>>> More seriously, this patch looks like it enables code which hasn't been
>>> used or tested before.  How well tested was this?
>>>
>>> Are there any runtime-visible effects from this change?
>>
>> I tested zswap on x86 and x86-64 and there was no difference. This is
>> good as there shouldn't be visible anything because swapoff is unusing
>> all pages anyway:
>> 	try_to_unuse(type, false, 0); /* force all pages to be unused */
>>
>> I haven't tested other frontswap users.
> 
> So is that code in __frontswap_invalidate_area() unneeded?
> 

I don't think so, it's still needed otherwise there will be memory leak.
I'm afraid nobody noticed the memory leak here before, this patch can
fix it. Sorry for didn't pay enough attention but please keep
__frontswap_invalidate_area().

-- 
Regards,
-Bob
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