linux-kernel - Re: question related page frame reclaim on embedded system

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Message-Id: <20081204191510.1D80.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Thu,  4 Dec 2008 19:16:42 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	mengsanshui@...oo.com.cn
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: question related page frame reclaim on embedded system

> 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 .

Yes.
if you don't free IPC share memory, it remain on the system until reboot.



> 
> Thanks advanced .
> Best Regards.
> Peter
> 
> 
> --- On Wed, 12/3/08, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 
> > From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > Subject: Re: question related page frame reclaim on embedded system
> > To: mengsanshui@...oo.com.cn
> > Cc: kosaki.motohiro@...fujitsu.com, linux-kernel@...r.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.
> 
> 
>       
> --
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