linux-kernel - Re: [PATCH v3 2/3] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently

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Date:	Sat, 12 Oct 2013 10:32:31 +0800
From:	Bob Liu <lliubbo@...il.com>
To:	Weijie Yang <weijie.yang@...sung.com>
Cc:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Bob Liu <bob.liu@...cle.com>,
	Weijie Yang <weijie.yang.kh@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org, d.j.shin@...sung.com,
	heesub.shin@...sung.com, Kyungmin Park <kyungmin.park@...sung.com>,
	hau.chen@...sung.com, bifeng.tong@...sung.com, rui.xie@...sung.com
Subject: Re: [PATCH v3 2/3] mm/zswap: bugfix: memory leak when invalidate and
 reclaim occur concurrently

On Thu, Sep 26, 2013 at 11:42 AM, Weijie Yang <weijie.yang@...sung.com> wrote:
> On Tue, Sep 24, 2013 at 9:03 AM, Minchan Kim <minchan@...nel.org> wrote:
>> On Mon, Sep 23, 2013 at 04:21:49PM +0800, Weijie Yang wrote:
>> >
>> > Modify:
>> >  - check the refcount in fail path, free memory if it is not referenced.
>>
>> Hmm, I don't like this because zswap refcount routine is already mess for me.
>> I'm not sure why it was designed from the beginning. I hope we should fix it first.
>>
>> 1. zswap_rb_serach could include zswap_entry_get semantic if it founds a entry from
>>    the tree. Of course, we should ranme it as find_get_zswap_entry like find_get_page.
>> 2. zswap_entry_put could hide resource free function like zswap_free_entry so that
>>    all of caller can use it easily following pattern.
>>
>>   find_get_zswap_entry
>>   ...
>>   ...
>>   zswap_entry_put
>>
>> Of course, zswap_entry_put have to check the entry is in the tree or not
>> so if someone already removes it from the tree, it should avoid double remove.
>>
>> One of the concern I can think is that approach extends critical section
>> but I think it would be no problem because more bottleneck would be [de]compress
>> functions. If it were really problem, we can mitigate a problem with moving
>> unnecessary functions out of zswap_free_entry because it seem to be rather
>> over-enginnering.
>
> I refactor the zswap refcount routine according to Minchan's idea.
> Here is the new patch, Any suggestion is welcomed.
>
> To Seth and Bob, would you please review it again?
>

I have nothing in addition to Minchan's review.

Since the code is a bit complex, I'd suggest you to split it into two patches.
[1/2]: fix the memory leak
[2/2]: clean up the entry_put

And run some testing..

Thanks,
-Bob
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