To: TaoMa <tao.ma@oracle.com>
Cc: Amerigo Wang <xiyou.wangcong@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Alexey Dobriyan <adobriyan@gmail.com>
References: <2375c9f90906072341o2cded749m45bdddfdb499469@mail.gmail.com>
	<4A2CC52B.9010602@oracle.com>
	<2375c9f90906081743p77934f47n8ba1a018d333b95b@mail.gmail.com>
	<m1ab4i11zx.fsf@fess.ebiederm.org>
	<20090611050929.GA2706@cr0.nay.redhat.com>
	<m11vpqvozl.fsf@fess.ebiederm.org> <20090613040958.GA2959@cr0>
	<m17hzg7oil.fsf@fess.ebiederm.org>
	<20090615021457.GA3388@cr0.nay.redhat.com> <4A35E32C.30609@oracle.com>
	<20090615070018.GD3544@cr0.nay.redhat.com>
	<4A360793.6060000@oracle.com> <m1ski1g632.fsf@fess.ebiederm.org>
	<4A36C6CA.9070507@oracle.com>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: Mon, 15 Jun 2009 12:48:13 -0700
In-Reply-To: <4A36C6CA.9070507@oracle.com> (TaoMa's message of "Tue\, 16 Jun 2009 06\:10\:18 +0800")
Message-ID: <m1eitl8eiq.fsf@fess.ebiederm.org>
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Subject: Re: [Patch BUGFIX] kcore: fix its wrong size on x86_64
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TaoMa <tao.ma@oracle.com> writes:

> ebiederm@xmission.com wrote:
>> Tao Ma <tao.ma@oracle.com> writes:
>>
>>   
>>> Hi Amerigo,
>>>
>>> The wrong number I mean is 131941393240064.
>>>
>>> So do you think
>>> [root@test3 ~]# ls -l /proc/kcore
>>> -r-------- 1 root root 131941393240064 Jun 15 13:39 /proc/kcore
>>>
>>> is better than
>>>
>>> [taoma@test2 ~]$ ll /proc/kcore
>>> -r-------- 1 root root 281474974617600 Jun 15 15:20 /proc/kcore
>>> ?
>>>
>>> I don't think so.
>>>
>>> Actually the right result should look like
>>>
>>> [root@test8 ~]# ls -l /proc/kcore
>>> -r-------- 1 root root 5301604352 Jun 15 13:35 /proc/kcore
>>>
>>> And with your patch I can't get this number.
>>>     
>>
>> Actually that value is the bug.  It has absolutely nothing
>> to do with the offsets that are valid within /proc/kcore.
>>
>> Why do you prefer the smaller number?
>>   
> Amerigo said in the previous e-mail that " the man page for/proc/kcore is wrong,
> its size can be more than the physical memory size, because it also contains
> memory area of vmalloc(), vsyscall etc..."
>
> I have 4G memory, and 5301604352 is just a bit larger than 4G and looks sane. So
> I misunderstand that this number is right.

It should also include the 32 Tebibyte range we have for vmalloc.  So
a completely dense encoding would be a bit larger than 35184372088832
bytes.  You can see that range in your readelf -l output.

Since the encoding is not dense the size actually comes to. 256TiB.
Or roughly 281474976710656 bytes.

> But if it is also a bug, I am willing to test any of the new patch. ;)

Not in the sense that anything could go wrong.  Merely in the sense that
we have a contradictory definition.  Which causes loads of confusion.

I am wondering if this difference in definition has caused any
problems applications to fail or if this just started out as an
observation of an anomaly?

Eric


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