linux-kernel - Re: [RFC][PATCH] vmscan: report vm_flags in page

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Message-ID: <20090517112550.GA3254@localhost>
Date:	Sun, 17 May 2009 19:25:50 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Elladan <elladan@...imo.com>, Nick Piggin <npiggin@...e.de>,
	Christoph Lameter <cl@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>
Subject: Re: [RFC][PATCH] vmscan: report vm_flags in page_referenced()

On Mon, May 11, 2009 at 07:45:00AM +0800, Minchan Kim wrote:
> Sorry for late. 
> 
> On Sat, 9 May 2009 14:56:40 +0800
> Wu Fengguang <fengguang.wu@...el.com> wrote:
> 
> > Hmm, this reminded me of the mlocked page protection logic in
> > page_referenced_one(). Why shall the "if (vma->vm_flags & VM_LOCKED)"
> > check be placed *after* the page_check_address() check? Is there a
> > case that an *existing* page frame is not mapped to the VM_LOCKED vma?
> > And why not to protect the page in such a case?
> 
> 
> I also have been having a question that routine.
> As annotation said, it seems to prevent increaseing referenced counter for mlocked page to move the page to unevictable list ASAP.
> Is right?

That's right. And it is only stopping the reference count for the
current VMA - if the reference count has already been elevated, the
mlocked page will continue to float in the [in]active lists.

> But now, page_referenced use refereced variable as just flag not count. 
> So, I think referecned variable counted is meaningless. 

Yes kind of, but anyway it costs nothing :-)

Thanks,
Fengguang

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