linux-kernel - Re: [RFC] Track mlock()ed pages

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Date:	Fri, 26 Jan 2007 03:13:00 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] Track mlock()ed pages

On Thu, 25 Jan 2007 22:36:17 -0800 (PST)
Christoph Lameter <clameter@....com> wrote:

> On Fri, 26 Jan 2007, Nick Piggin wrote:
> 
> > Christoph Lameter wrote:
> > > Add NR_MLOCK
> > > 
> > > Track mlocked pages via a ZVC

Why?

> > I think it is not quite right. You are tracking the number of ptes
> > that point to mlocked pages, which can be >= the actual number of pages.
> 
> Mlocked pages are not inherited. I would expect sharing to be very rare.
>  
> > Also, page_add_anon_rmap still needs to be balanced with page_remove_rmap.
> 
> Hmmm.... 
>  
> > I can't think of an easy way to do this without per-page state. ie.
> > another page flag.
> 
> Thats what I am trying to avoid.

You could perhaps go for a walk across all the other vmas which presently
map this page.  If any of them have VM_LOCKED, don't increment the counter.
Similar on removal: only decrement the counter when the final mlocked VMA
is dropping the pte.

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