linux-kernel - Re: [PATCH 02/10] zcache: fix refcount leak

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Message-ID: <4FE27C9B.2070500@linux.vnet.ibm.com>
Date:	Thu, 21 Jun 2012 09:44:59 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Konrad Wilk <konrad.wilk@...cle.com>,
	Nitin Gupta <ngupta@...are.org>
Subject: Re: [PATCH 02/10] zcache: fix refcount leak

On 06/21/2012 06:25 AM, Dan Magenheimer wrote:

>> From: Xiao Guangrong [mailto:xiaoguangrong@...ux.vnet.ibm.com]
>> Subject: Re: [PATCH 02/10] zcache: fix refcount leak
>>
>> On 06/20/2012 10:54 AM, Xiao Guangrong wrote:
>>
>>> On 06/20/2012 04:06 AM, Seth Jennings wrote:
>>>
>>>> On 06/19/2012 02:49 PM, Dan Magenheimer wrote:
>>>>
>>>>> My preference would be to fix it the opposite way, by
>>>>> checking and ignoring zcache_host in zcache_put_pool.
>>>>> The ref-counting is to ensure that a client isn't
>>>>> accidentally destroyed while in use (for multiple-client
>>>>> users such as ramster and kvm) and since zcache_host is a static
>>>>> struct, it should never be deleted so need not be ref-counted.
>>>>
>>>>
>>>> If we do that, we'll need to comment it.  If we don't, it won't be
>>>> obvious why we are refcounting every zcache client except one.  It'll
>>>> look like a bug.
>>>
>>>
>>> Okay, i will fix it like Dan's way and comment it.
>>
>> Hmm...But i notice that zcache_host is the same as other clients, all
>> of them are static struct:
>>
>> | static struct zcache_client zcache_host;
>> | static struct zcache_client zcache_clients[MAX_CLIENTS];
>>
>> And all of them are not destroyed.
> 
> Yes, the code currently in zcache was a first step towards
> supporting multiple clients.  Ramster goes one step further
> and kvm will require even a tiny bit more work.
> 


So, do you mind we increase the refcount for all clients (zcache host and
other clients) first? Like my origin patch?

> FYI, I'm working on a unification version of zcache that can support
> all of these cleanly as well as better support for eviction
> that will make standalone zcache more suitable for promotion from
> staging and enterprise-ready.  Due to various summer commitments,
> it will probably be a few weeks before it is ready for posting.


Great work, look forward to the progress! :)

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