linux-kernel - Re: [RFC] some page can't be migrated

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Message-ID: <Pine.LNX.4.64.0801281514260.17050@schroedinger.engr.sgi.com>
Date:	Mon, 28 Jan 2008 15:17:38 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Shaohua Li <shaohua.li@...el.com>, nickpiggin@...oo.com.au,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] some page can't be migrated

On Sat, 26 Jan 2008, Andrew Morton wrote:

> > 
> > -	if (!page->mapping)
> > +	if (!page->mapping) {
> > +		if (!PageAnon(page) && PagePrivate(page))
> > +			try_to_release_page(page, GFP_KERNEL);
> >  		goto rcu_unlock;
> > +	}
> 
> We call something(GFP_KERNEL) under rcu_read_lock()?  I've lost track of
> the myriad flavours of rcu which we purport to support, but I don't think
> they'll all like us blocking under rcu_read_lock().

I still think your solution is good but even with the original patch we do 
not call try_to_release_page() with GFP_KERNEL under rcu.

   if (PageAnon(page)) {
                rcu_read_lock();
                rcu_locked = 1;
        }


rcu is only active if we have an anonymous page and in that case we do not
call try_to_release_page(). Just to make sure that Nick and I do not get 
dinged needlessly....

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