Date: Mon, 28 Jan 2008 11:09:09 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: Andrew Morton <akpm@linux-foundation.org>
cc: Shaohua Li <shaohua.li@intel.com>, nickpiggin@yahoo.com.au,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC] some page can't be migrated
In-Reply-To: <20080126220351.a04819f9.akpm@linux-foundation.org>
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On Sat, 26 Jan 2008, Andrew Morton wrote:

> 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().
> 
> We _won't_ block, because try_to_release_page() will see the NULL ->mapping
> and will call the non-blocking try_to_free_buffers().  But still, it looks
> bad, and will cause problems if someone decides to add a might_sleep_if()
> to try_to_release_page().
> 
> So...  I'd suggest that it would be better to add an apologetic comment and
> call direct into try_to_free_buffers().

Right. Looks good. PageWriteback cannot be set if we do not have a 
mappig...

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