Re: question related page frame reclaim on embedded system

[peter meng <mengsanshui@yahoo.com.cn>]

Hi,Kosaki

1. what happens if used IPC share memory ?
   As i knew IPC share memory  use anonymous mapping ,but not sure my understand is correctly .

Thanks advanced .
Best Regards.
Peter


--- On Wed, 12/3/08, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Subject: Re: question related page frame reclaim on embedded system
> To: mengsanshui@yahoo.com.cn
> Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org
> Date: Wednesday, December 3, 2008, 9:48 AM
> > 
> > Hi,Kosaki
> > 
> > Thank you very much .
> > I have another question about share memory . Assume a
> process create a share memory ,
> > seems the page that the process used can not be
> discard or swap out
> 
> No. Linux can swap out COW shared memory too. see swap
> cache related code.
> Also, Linux can discard non-dirty and file mapped shared
> page.
> 
> but, yes.
> Linux can't discart dirty or anonymous mapped page.
> 
> 
> > when they are no longer used by any process or no swap
> space .
> > 
> > 1.whether the maped page of the share memory is
> persistent in system until
> >   system restart ? if not how page frame reclaiming
> process it ? 
> 
> No.
> Linux manage page reference count.
> forrk increment it. exit decrement it.
> So, when process exiting, Linux can discard non used page
> immediately.
> 
> IOW, reclaim provide "page discard/swap although page
> is still used" mechanism.