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Date: Tue, 4 Apr 2006 08:20:03 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
To: Nick Piggin <npiggin@suse.de>
cc: Andrew Morton <akpm@osdl.org>, Linux Kernel <linux-kernel@vger.kernel.org>,
       Linux Memory Management <linux-mm@kvack.org>
Subject: Re: [patch 2/3] mm: speculative get_page
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Looks like the NoNewRefs flag is mostly == 
spin_is_locked(mapping->tree_lock)? Would it not be better to check the 
tree_lock?


> --- linux-2.6.orig/mm/migrate.c
> +++ linux-2.6/mm/migrate.c
>  
> +	SetPageNoNewRefs(page);
>  	write_lock_irq(&mapping->tree_lock);

A dream come true! If this is really working as it sounds then we can 
move the SetPageNoNewRefs up and avoid the final check under 
mapping->tree_lock. Then keep SetPageNoNewRefs until the page has been 
copied. It would basically play the same role as locking the page.