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.
prev parent reply other threads:[~2012-09-04 8:48 UTC|newest]
Thread overview: 7+ 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]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5045C06F.4000507@gmail.com \
--to=xiyou.wangcong@gmail.com \
--cc=jkosina@suse.cz \
--cc=linux-kernel@vger.kernel.org \
--cc=xerox.time.tech@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).