linux-kernel - Re: [PATCH v2 2/2] btrfs-progs: Fix up memory leakage

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Message-ID: <CAEH94LirayD_NB2KW5q5KSZ3nVTJLYpi23D_ioGwcKmn0WyDVw@mail.gmail.com>
Date:	Wed, 26 Sep 2012 10:58:26 +0800
From:	Zhi Yong Wu <zwu.kernel@...il.com>
To:	kreijack@...ind.it
Cc:	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	jbacik@...ionio.com, dave@...os.cz, linuxram@...ux.vnet.ibm.com,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2/2] btrfs-progs: Fix up memory leakage

On Wed, Sep 26, 2012 at 1:14 AM, Goffredo Baroncelli <kreijack@...ero.it> wrote:
> On 09/25/2012 12:14 PM, David Sterba wrote:
>>
>> On Tue, Sep 25, 2012 at 10:02:16AM +0800, zwu.kernel@...il.com wrote:
>>>
>>> From: Zhi Yong Wu<wuzhy@...ux.vnet.ibm.com>
>>>
>>>    Some code pathes forget to free memory on exit.
>>
>>
>> Same as with the fd's, kernel will free all memory for us at exit().
>
>
> I strongly disagree with this approach. The callee often don't know what
> happen after and before the call. The same is true for the programmer,
> because the code is quite often updated by several people. A clean exit() is
> the right thing to do as general rule. I don't see any valid reason (in the
> btrfs context) to do otherwise.
>
> Relying on the exit() for a proper clean-up increase the likelihood of bug
> when the code evolves (see my patch   [RESPOST][BTRFS-PROGS][PATCH]
> btrfs_read_dev_super(): uninitialized variable for an example of what means
> an incorrect deallocation of resource).
>
>
>> If there's lots of memory allocated, it may be even faster to leave the
>> unallocation process to kernel as it will do it in one go, while the
>> application would unnecessarily free it chunk by chunk.
>
>
> May be I am wrong, but I don't think that the increase of speed of the btrfs
> "command" is even measurable relying on exit instead of free()-ing each
> chunk of memory one at time.... The same should be true for the
> open()/close()

I fully agree with you. In one same function, i find that some code
path free system sources,
while other code path doesn't. This is one nice way.

>
> My 2¢
>
> BR
> G.Baroncelli
>
>>
>> david
>> --
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>> .
>>
>



-- 
Regards,

Zhi Yong Wu
--
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