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From: Cong Wang <xiyou.wangcong@gmail.com>
To: Jiri Kosina <jkosina@suse.cz>
Cc: Xin Tong <xerox.time.tech@gmail.com>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: linux page table
Date: Tue, 04 Sep 2012 16:48:47 +0800	[thread overview]
Message-ID: <5045C06F.4000507@gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.00.1209022026100.20709@pobox.suse.cz>

On 09/03/2012 02:26 AM, Jiri Kosina wrote:
> On Sun, 2 Sep 2012, Xin Tong wrote:
>
>>>> 3. can two different processes have their CR3 being the same value
>>>> even though they have different first level page tables ?
>>>
>>> Yes, if they are created by clone(CLONE_VM). In such case they share the
>>> same mm_struct, and therefore mm_struct->pgd (which is exactly what is
>>> loaded into cr3 in switch_mm()) is the same.
>>>
>>
>> Is this the COW mechanism in linux. what if the cloned process need to
>> have set of its own pages later. do the CR3s for the 2 processes
>> become different at that point ?
>
> That is a different story. COW is applied on fork() (i.e. spawning new
> process), not on clone(CLONE_VM) (i.e. spawning new thread).
>

Yeah, and unshare(2) does not implement the flag that reverses the 
effects of CLONE_VM.


  reply	other threads:[~2012-09-04  8:48 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-01 19:30 linux page table Xin Tong
2012-09-01 20:01 ` Shentino
2012-09-01 20:12   ` Xin Tong
2012-09-02  8:10 ` Jiri Kosina
2012-09-02 15:56   ` Xin Tong
2012-09-02 18:26     ` Jiri Kosina
2012-09-04  8:48       ` Cong Wang [this message]
  -- strict thread matches above, loose matches on Subject: below --
2002-06-17 15:58 anya aitali
2002-06-17 23:19 ` William Lee Irwin III
2002-06-17 23:25 ` William Lee Irwin III

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