linux-kernel - Re: [patch 1/2] mm: speculative get

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Message-ID: <20060801204202.GA223@oleg>
Date:	Wed, 2 Aug 2006 00:42:02 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Dave Kleikamp <shaggy@...tin.ibm.com>
Cc:	Nick Piggin <npiggin@...e.de>, Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...l.org>,
	Andy Whitcroft <apw@...dowen.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] mm: speculative get_page

On 08/01, Dave Kleikamp wrote:
>
> On Tue, 2006-08-01 at 23:32 +0400, Oleg Nesterov wrote:
> > Nick Piggin wrote:
> > >
> > > --- linux-2.6.orig/mm/vmscan.c
> > > +++ linux-2.6/mm/vmscan.c
> > > @@ -380,6 +380,8 @@ int remove_mapping(struct address_space 
> > >  	if (!mapping)
> > >  		return 0;		/* truncate got there first */
> > >
> > > +	SetPageNoNewRefs(page);
> > > +	smp_wmb();
> > >  	write_lock_irq(&mapping->tree_lock);
> > >
> > 
> > Is it enough?
> > 
> > PG_nonewrefs could be already set by another add_to_page_cache()/remove_mapping(),
> > and it will be cleared when we take ->tree_lock.
> 
> Isn't the page locked when calling remove_mapping()?  It looks like
> SetPageNoNewRefs & ClearPageNoNewRefs are called in safe places.  Either
> the page is locked, or it's newly allocated.  I could have missed
> something, though.

No, I think it is I who missed something, thanks.

Oleg.

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